enVision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume

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enVision Math Common Core 8th Grade Answers Key Topic 8 Solve Problems Involving Surface Area And Volume

Topic 8 Essential Question
How can you find volumes and surface areas of three-dimensional figures?
Answer:
The “Surface area” is the sum of the areas of all faces (or surfaces) on a 3D shape.
Ex:
A cuboid has 6 rectangular faces. To find the surface area of a cuboid, add the areas of all 6 faces
We know that,
The volume of a three-dimensional figure = Cross-sectional area × length

3-ACT MATH

Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 1
Measure Up
Have you ever heard of the terms griffin beaker, Erlenmeyer flask, or graduated cylinder? Maybe you’ve used them in your science class. Each piece of equipment in a chemistry lab has a specific purpose, so containers come in many shapes. It’s sometimes necessary to pour a solution from one container to another. Think about this during the 3-Act Mathematical Modeling lesson.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 2

Topic 8 ënVision STEM Project

Did You Know?
The production of packaging is a huge industry employing over five million people with annual sales of more than 400 billion dollars.
Packaging materials protect and deliver food and products to consumers.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 3

A plastic bottle takes 450–1,000 years to biodegrade.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 4
Seabirds are dying of starvation with stomachs full of plastic and Styrofoam.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 5

Polystyrene foam lasts forever!
Eco-friendly packaging materials are being made from mushrooms and bamboo.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 6
There is even a drink bottle made from recyclable paper.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 7
New technology results in packaging materials that are both affordable and biodegradable.
Environmentally friendly companies are producing sustainable packaging. In addition to using recyclable materials, they reduce the water, natural resources, and energy needed for production. They minimize waste when designing products.

Your Task: Wrap it Up!
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 8
Engineers consider several factors when designing product packaging. These factors include cost efficiency and eco-friendly design so that materials are disposable, recyclable, biodegradable, and not wasted. Suppose you are an engineer working for Liquid Assets, an environmentally friendly company that designs, builds, and packages water purifiers. You and your classmates will use your knowledge of volume and surface area to determine an environmentally sound way to package the purifiers.

Topic 8 GET READY!

Review What You Know!

Vocabulary
Choose the best term from the box to complete each definition.
base
diameter
radius
three-dimensional
two-dimensional

Question 1.
The __________ is the distance from the center to the edge of a circle.
Answer:
We know that,
The “Radius” is the distance from the center to the edge of a circle
Hence, from the above,
We can conclude that the best term to complete the given definition is: Radius

Question 2.
A shape that has length, width, and height is ___________.
Answer:
We know that,
A shape that has a length, width, and height is known as “Three-dimensional”
Hence, from the above,
We can conclude that the best term to complete the given definition is: Three dimensional

Question 3.
Any side of a cube can be considered a __________.
Answer:
We know that,
Any side of a cube can be considered a “Base”
Hence, from the above,
We can conclude that the best term to complete the given definition is: Base

Question 4.
A shape that has length and width, but not height, is ___________.
Answer:
We know that,
A shape that has length and width, but not height is known as “Two-dimensional”
Hence, from the above,
We can conclude that the best term to complete the given definition is: Two-dimensional

Question 5.
The _____________ of a circle is a line segment that passes through its center and has endpoints on the circle.
Answer:
We know that,
The “Diameter” of a circle is a line segment that passed through its center and has endpoints on the circle
Hence, from the above,
We can conclude that the best term to complete the given definition is: Diameter

Multiplying with Decimals

Find the product.
Question 6.
14 ∙ 3.5 = _______
Answer:
The given expression is:
14 × 3.5
So,
14 × 3.5 = 49.0
Hence, from the above,
We can conclude that the value for the given expression is: 49

Question 7.
9 ∙ 3.14 = _________
Answer:
The given expression is:
9 × 3.14
So,
9 × 3.14 = 28.26
Hence, from the above,
We can conclude that the value for the given expression is: 28.26

Question 8.
4.2 ∙ 10.5 = _________
Answer:
The given expression is:
4.2 × 10.5
So,
4.2 × 10.5 = 44.1
Hence, from the above,
We can conclude that the value for the given expression is: 44.1

Areas of Circles

Find the area of each circle. Use 3.14 for π.
Question 9.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 9
A = ________
Answer:
The given circle is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 9
From the given circle,
The radius is: 8 cm
Now,
We know that,
The area of the circle = πr²
So,
The area of the given circle = 3.14 × 8²
= 200.96 cm²
Hence, from the above,
We can conclude that the area for the given circle is: 200.96 cm²

Question 10.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 10
A = _________
Answer:
The given circle is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 10
From the given circle,
The diameter is: 12 cm
Now,
We know that,
Radius = \(\frac{Diameter}{2}\)
Radius = \(\frac{12}{2}\)
Radius = 6 cm
Now,
We know that,
The area of the circle = πr²
So,
The area of the given circle = 3.14 × 6²
= 113.04 cm²
Hence, from the above,
We can conclude that the area of the given circle is: 113.04 cm²

Use the Pythagorean Theorem

Find the missing side length of the triangle.
Question 11.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 11
x = _________
Answer:
The given triangle is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 11
Now,
Fro the given figure,
We can observe that the triangle is a right triangle
Now,
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the length of the hypotenuse
a and b are the side lengths
So,
13² = 12²+ x²
x²= 169 – 144
x² = 25
x = \(\sqrt{25}\)
x = 5 in.
Hence, from the above,
We can conclude that the missing side length of the given triangle is: 5 in.

Question 12.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 12
x = __________
Answer:
The given triangle is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 12
Now,
Fro the given figure,
We can observe that the triangle is a right triangle
Now,
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the length of the hypotenuse
a and b are the side lengths
So,
30² = 24²+ x²
x²= 900 – 576
x² = 324
x = \(\sqrt{324}\)
x = 18 in.
Hence, from the above,
We can conclude that the missing side length of the given triangle is: 18 in.

Language Development

Complete the word web. Write keywords, ideas, examples, or illustrations that connect to each new vocabulary term.

Topic 8 Pick A Project

PROJECT 8A
What makes a concert rock?
PROJECT: DESIGN PROPS OR STAGE STRUCTURES
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 15

PROJECT 8B
What is the most interesting museum you have visited?
PROJECT: MAKE A MODEL OF A MUSEUM
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 16

PROJECT 8C
Where around the United States can you find quarries?
PROJECT: POUR AND MEASURE SAND
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 17

PROJECT 8D
If you were cast in a play, would it be a comedy or a drama? Why?
PROJECT: WRITE A SKIT
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 18

Lesson 8.1 Find Surface Area of Three-Dimensional Figures

Explore It!
Andrea is designing the packaging for a tube-shaped container.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 19
I can… find the surface areas of cylinders, cones, and spheres.

A. Model with Math What two-dimensional shape represents the top and bottom of the container? What two-dimensional shape represents the tube? Draw a net of the tube-shaped container.
Answer:
It is given that Andrea is designing the packaging for a tube-shaped container.
Now,
The given arrangement for tube shaped container is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 19
Now,
From the given arrangement,
We can observe that
The two-dimensional shape that represents the top and bottom of the container is: Circle
The two-dimensional shape that represents the tube is: Rectangle
Hence,
The representation of the tube-shaped container is:

B. Look for Relationships The circular top and bottom fit perfectly on the ends of the container. How are the measures of the circles and the rectangle related?
Answer:
The representation of the tube-shaped container is:

Now,
From the given figure,
We can observe that the tube-shaped container is made up of 2 circles and 1 rectangle
So,
The total surface area of the tube-shaped container is the sum of the areas of 2 circles and 1 rectangle
Now,
We know that,
The area of a circle = πr²
The area of a rectangle = Height× Base
Where,
The base of the rectangle is a circle
So,
The circumference of the circle = 2πr
Hence,
The surface area of the tube-shaped container = 2πr² + 2πrh

Focus on math practices
Model with Math
How can you check whether the net that you drew accurately represents the tube-shaped container?
Answer:
The representation of the tube-shaped container is:

Now,
When the top and bottom of the container correctly fit the tube,
That is the representation that the net you drew accurately represents the tube-shaped container

Essential Question
How are the areas of polygons used to find the surface area formulas for three-dimensional figures?
Answer:
We know that,
A three-dimensional figure is a combination of some two-dimensional figures
Ex:
We can make a “Cuboid” from the combination of “Rectangles”
We can make a “Sphere” from the combination of ‘Circles”
So,
The total surface area of a three-dimensional figure can be given as the sum of all the areas of the two-dimensional figures that are used to make the three-dimensional figure

Try it

What is the surface area of a cylinder with a height of 9.5 inches and a radius of 2.5 inches?
The surface area of the cylinder is __________ square inches.
Answer:
It is given that
The height of a cylinder is: 9.5 inches
The radius of a cylinder is: 2.5 inches
Now,
We know that,
The surface area of the cylinder (S.A) = 2πr² + 2πrh
= 2 × 3.14 × (2.5)² + 2 × 3.14 × 9.5 × 2.5
= 39.25 + 149.15
= 188.4 square inches
Hence, from the above,
We can conclude that the surface area of the given cylinder is: 188.4 square inches

Convince Me! How can you find the surface area of a cylinder if you only know its height and the circumference of its base?
S.A. = 2(πr2) + (2πr)h
= 2π(________2) + 2π(_______)(________)
= _______π + _______π
= _______π
Answer:
It is given that
We know only the height of the cylinder and the circumference of its base
Now,
We know that,
The surface area of a cylinder (S.A) = 2πr² + 2πrh
So,
S.A = 2π (r²) + 2π (r) (h)
S.A = 2π + π
S.A = 3π
Hence, from the above,
We can conclude that the surface area of a cylinder with only its height and the circumference of its base is: 3π

Try It!

a. What is the surface area of a cone with a radius of 7 feet and a slant height of 9 feet? Use \(\frac{22}{7}\) for π.
Answer:
It is given that
The radius of the cone is (r): 7 feet
The slant height of the cone is (l): 9 feet
Now,
We know that,
The surface area of the cone (S.A) = πr² + πrl
So,
S.A = \(\frac{22}{7}\) × 7² + \(\frac{22}{7}\) × 7 × 9
= 154 + 198
= 352 square feet
Hence, from the above,
We can conclude that the surface area of the given cone is: 352 square feet

b. What is the surface area of a sphere with a diameter of 2.7 inches? Use 3.14 for π.
Answer:
It is given that,
The diameter of a sphere is: 2.7 inches
Now,
We know that,
Radius = \(\frac{Diameter}{2}\)
So,
Radius of the sphere = \(\frac{2.7}{2}\)
So,
The radius of the sphere (r) = 1.35 inches
Now,
We know that,
The surface area of the sphere (S.A) = 4πr²
So,
S.A = 4 × 3.14 × (1.35)²
= 22.89 square inches
Hence, from the above,
We can conclude that the surface area of the given sphere is: 22.89 square inches

KEY CONCEPT

Formulas for finding the area of polygons can be used to find the surface areas of cylinders, cones, and spheres.

Do You Understand?
Question 1.
Essential Question How are the areas of polygons used to find the surface area formulas for three-dimensional figures?
Answer:
We know that,
A three-dimensional figure is a combination of some two-dimensional figures
Ex:
We can make a “Cuboid” from the combination of “Rectangles”
We can make a “Sphere” from the combination of ‘Circles”
So,
The total surface area of a three-dimensional figure can be given as the sum of all the areas of the two-dimensional figures that are used to make the three-dimensional figure

Question 2.
Reasoning Why is the length of the base of the rectangle the same as the circumference of the circles in the net of a cylinder?
Answer:
The representation of the cylinder is:

Now,
If you look at the net, the curved surface of the cylinder is rectangular in shape. The length of the rectangle is the same as the circumference of the circle. Since the length of the rectangle wraps around the circle rim, it is the same length as the circumference of the circle.

Question 3.
Construct Arguments Aaron says that all cones with a base circumference of 8 inches will have the same surface area. Is Aaron correct? Explain.
Answer:
It is given that
Aaron says that all cones with a base circumference of 8 inches will have the same surface area
Now,
We know that,
The surface area of a cone = πr² + πrl
Now,
From the above formula,
We can conclude that the surface area of the cone does not depend only on the circumference of the base but also we need the side length of the cone part as well
So,
All cones with a base circumference of 8 inches will not have the same surface area.
Hence, from the above,
We can conclude that Aaron is not correct

Do You Know How?
Question 4.
What is the surface area of the cylinder? Use 3.14 for π, and round to the nearest tenth.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 20
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 20
From the given figure,
The diameter of the cylinder is: 2 mm
The height of the cylinder is: 10 mm
So,
Radius of the cylinder = \(\frac{Diameter of the cylinder}{2}\)
= \(\frac{2}{2}\)
= 1 mm
Now,
We know that,
The surface area of the cylinder (S.A) = 2πr² + 2πrh
So,
S.A = 2 × 3.14 × 1² + 2 × 3.14 × 1 × 10
= 6.28 + 62.8
= 69.08 mm²
Hence, from the above,
We can conclude that the surface area of the given cylinder is: 69.08 mm²

Question 5.
What is the surface area of the cone to the nearest tenth? Use 3.14 for π.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 21
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 21
From the given figure,
The slant height of the cone is (l): 4 ft
The radius of the cone is: 3 ft
Now,
We know that,
The surface area of the cone (S.A) = πr² + πrl
So,
S.A = 3.14 × 3² + 3.14 × 3 × 4
= 28.26 + 37.68
= 65.94 ft²
Hence, from the above,
We can conclude that the surface area of the given cone is: 65.94 ft²

Question 6.
What is the surface area of the sphere in terms of π?
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 22
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 22
From the given figure,
The diameter of the sphere is: 2 cm
Now,
We know that,
The radius of the sphere (r) = \(\frac{Diameter of the sphere}{2}\)
= \(\frac{2}{2}\)
= 1 cm
Now,
We know that,
The surface area of the sphere (S.A) = 4πr²
So,
S.A = 4 × 3.14 × 1²
= 12.56 cm²
Hence, from the above,
We can conclude that the surface area of the given sphere is: 12.56 cm²

Practice & Problem Solving

Leveled Practice In 7-8, find the surface area.
Question 7.
What is the surface area of the cylinder? Use 3.14 for π, and round to the nearest tenth.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 23
S.A. = 2(πr2) + (2πr)h
= 2π(________2) + 2 π(_______)(________)
= 2 π(________) + 2 π(_________)
= _______π + _______π
= _______π
≈ ________ cm2
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 23
From the given figure,
The radius of the cylinder is: 3 cm
The height of the cylinder is: 5 cm
Now,
We know that,
The surface area of the cylinder (S.A) = 2πr² + 2πrh
So,
S.A = 2 × 3.14 × 3² + 2 × 3.14 × 3 × 5
= 56.52 + 94.2
= 150.72 cm²
Hence, from the above,
We can conclude that the surface area of the given cylinder is: 150.72 cm²

Question 8.
What is the surface area of the cone? Use 3.14 for π.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 24
S.A. = πr2 + πlr
= π(________2) + π(_______)(________)
= ________ π + _________π
= _______π
≈ ________ cm2
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 24
From the given figure,
The radius of the cone (r) is: 7 cm
The slant height of the cone (l) is: 13 cm
Now,
We know that,
The surface area of the cone (S.A) = πr² + πrl
So,
S.A = 3.14 × 7² + 3.14 × 7 × 13
= 153.86 + 285.74
= 439.6 cm²
Hence, from the above,
We can conclude that the surface area of the given cone is: 439.6 cm²

Question 9.
Construct Arguments Sasha incorrectly claimed that the surface area of the cylinder is about 76.9 square inches. Explain her likely error and find the correct surface area of the cylinder.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 25
Answer
The given figure is:
:Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 25
Now,
From the given figure,
The diameter of the cylinder is: 7 in.
The height of the cylinder is: 19 in.
Now,
We know that,
Radius = \(\frac{Diameter}{2}\)
So,
Radius of the circle = \(\frac{7}{2}\)
= 3.5 in.
Now,
We know that,
The surface area of the cylinder (S.A) = 2πr² + 2πrh
So,
S.A = 2 × 3.14 × (3.5)² + 2 × 3.14 × 3.5 × 19
= 76.93 + 417.62
= 494.55 in.²
Hence, from the above,
We can conclude that
The correct surface area of the given cylinder is: 494.55 in.²
The mistake made by Sasha is:
She adds only the area of the top and bottom but not the area of the rectangle and the area of the top and bottom of the cylinder

Question 10.
A theme park has a ride that is located in half a sphere. The ride goes around the widest part of the sphere, which has a circumference of 514.96 yards. What is the surface area of the sphere? Estimate to the nearest hundredth using 3.14 for π.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 26
Answer:
It is given that
A theme park has a ride that is located in half a sphere. The ride goes around the widest part of the sphere, which has a circumference of 514.96 yards
Now,
The given sphere is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 26
Now,
We know that,
Circumference = 2πr
So,
Circumference of the theme park = 514.96 yd
2πr = 514.96
r = \(\frac{514.96}{2 × 3.14}\)
= 2.38 yd
Now,
We know that,
The surface area of the sphere (S.A) = 4πr²
So,
S.A = 4 × 3.14 × (2.38)²
= 71.14 yd²
Hence, from the above,
We can conclude that the surface area of the given sphere is: 71.14 yd²

Question 11.
Find the amount of wrapping paper you need to wrap a gift in the cylindrical box shown. You need to cover the top, the bottom, and all the way around the box. Use 3.14 for π, and round to the nearest tenth.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 27
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 27
Now,
From the given figure,
The radius of the cylinder is 9 in.
The height of the cylinder is: 8 in
Now,
We know that,
The surface area of the cylinder (S.A) = 2πr² + 2πrh
So,
S.A = 2 × 3.14 × 9² + 2 × 3.14 × 9 × 8
= 508.68 + 452.16
= 960.84 in.²
Hence, from the above,
We can conclude that the amount of wrapping paper you need to wrap a gift in the cylindrical box is: 960.84 in.²

Question 12.
Donna paints ornaments for a school play. Each ornament is made up of two identical cones, as shown. How many bottles of paint does she need to paint 70 ornaments?
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 28
Answer:
It is given that
Donna paints ornaments for a school play. Each ornament is made up of two identical cones, as shown
Now,
From the given figure,
We can observe that
The radius of a cone is: 4.1 cm
The slant height of a cone is: 8.9 cm
Now,
We know that,
The surface area of a cone (S.A) = πr² + πrl
So,
S.A = 3.14 × (4.1)² + 3.14 × 4.1 × 8.9
= 52.78 + 114.57
= 167.35 cm²
So,
The surface area of the second cone (S.A) = 167.35 cm²
So,
The S.A of 70 ornaments = 70 × (167.35 × 2)
= 23,429 cm²
So,
The number of bottles of paint she needed to paint 70 ornaments = \(\frac{23,429}{2,000}\)
= 11.7
≅ 12 bottles
Hence, from the above,
We can conclude that she need 12 bottles of paint to paint 70 ornaments

Question 13.
Higher-Order Thinking
a. What is the surface area of the cone? Use 3.14 for π, and round to the nearest whole number.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 29
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 29
Now,
From the given figure,
The diameter of the cone is: 6 cm
The slant height of the cone is: 12 cm
Now,
We know that,
Radius = \(\frac{Diameter}{2}\)
Radius = \(\frac{6}{2}\)
Radius = 3 cm
Now,
We know that,
The surface area of the cone (S.A) = πr² + πrl
So,
S.A = 3.14 × 3² + 3.14 × 3 × 12
= 28.26 + 113.04
= 141.3 cm²
Hence, from the above,
We can conclude that the surface area of the given cone is: 141.3 cm²

b. Reasoning Suppose the diameter and the slant height of the cone are cut in half. How does this affect the surface area of the cone? Explain.
Answer:
It is given that the diameter and the slant height of the cone are cut in half
So,
S.A = π(\(\frac{d}{2}\))² + π (\(\frac{d}{2}\)) (\(\frac{l}{2}\))
= 3.14 × \(\frac{6²}{4}\) + 3.14 × 3 × 6
= 28.26 + 56.52
= 84.78 cm²
Now,
From part (a),
The S.A of the cone is: 141.3 cm²
So,
The ratio of S.A of the cones obtained from part (a) and part (b) respectively = \(\frac{141.3}{84.78}\)
= 1.666
Hence, from the above,
We can conclude that the S.A of the cone we obtained in part (b) is 1.666 times of the S.A of the cone we obtained in part (b)

Assessment Practice
Question 14.
What is the surface area of the sphere? Use 3.14 for π, and round to the nearest tenth.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 30
A 254.5 cm2
B. 56.55 cm2
C. 1,017.4 cm2
D. 4,071.5 cm2
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 30
From the given figure,
The radius of the sphere is: 9 cm
Now,
We know that,
The surface area of the sphere (S.A) = 4πr²
So,
S.A = 4 × 3.14 × 9²
= 1,017.36 cm²
≈ 1,017.4 cm²
Hence, from the above,
We can conclude that the S.A of the given sphere is: 1,017.4 cm²

Question 15.
What is the approximate surface area of the cone, in square inches? Use 3.14 for π, and round to the nearest whole number.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 31
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 31
Now,
From the given figure,
The slant height of the cone (l) is 40 in.
The diameter of the cone (d) is 40 in.
Now,
We know that,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{40}{2}\)
r = 20 in.
Now,
We know that,
The surface area of the cone (S.A) = πr² + πrl
So,
S.A = 3.14 × 20² + 3.14 × 20 × 40
= 1,256 + 2,512
= 3,768 in.²
Hence, from the above,
We can conclude that the surface area of the given cone is: 3,768 in²

Lesson 8.2 Find Volume of Cylinders

Explain It!
Jenna and Ricardo are buying a new fish tank for the growing population of zebrafish in their science lab. Jenna says the tanks hold the same amount of water because they have the same dimensions. Ricardo says that he can fill the bottom of the rectangular tank with more cubes, so it can hold more water.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 32
I can… use what I know about finding volumes of rectangular prisms to find the volume of a cylinder.

A. Look for Relationships How are the shapes of the two fish tanks alike? How are they different?
Answer:
When we observe the fish tanks of Jenna and Ricardo,
We can observe that
a. The heights of the two fish tanks are the same
b. The number of cubes that can be filled at the bottom is different
c. The number of cubes filled in Jenna’s fish tank is less than that of the number of cubes filled in Ricardo’s fish tank
d. The amount of water that can hold in Jenna’s fish tank is less than the amount of water that can hold in Ricardo’s fish tank

B. Critique Arguments Who do you think is correct, Ricardo or Jenna? Explain.
Answer:
It is given that
Jenna and Ricardo are buying a new fish tank for the growing population of zebrafish in their science lab. Jenna says the tanks hold the same amount of water because they have the same dimensions. Ricardo says that he can fill the bottom of the rectangular tank with more cubes, so it can hold more water.
Now,
To find which fish tank holds more water, find the volume of the two fish tanks
Now,
For Jenna’s fish tank:
The fish tank is in the form of a cylinder
Now,
We know that,
The volume of the cylinder (V) = πr²h
= \(\frac{πd²h}{4}\)
So,
V = \(\frac{3.14 × 24 × 24 × 48}{4}\)
= \(\frac{86,814.72}{4}\)
= 21,073.68 in³
For Ricardo’s fish tank:
The fish tank is in the form of a rectangular prism
Now,
We know that,
The volume of a rectangular prism (V) = Length × Width × Height
So,
V = 24 × 24 × 48
= 27,648 in³
Hence, from the above,
We can conclude that Ricardo is correct on the basis of volumes of their fish tanks

Focus on math practices
Use Structure How can you use what you know about areas of two-dimensional figures and volumes of prisms to compare the volumes of the fish tanks?
Answer:
We know that,
Volume = Area × Length (or) Height (or) Depth
Where,
“Area” is the area of two-dimensional figures like rectangles, circles, etc.

Essential Question
How is the volume of a cylinder related to the volume of a rectangular prism?
Answer:
Rectangular prisms and cylinders are somewhat similar because they both have two bases and a height.
The formula for the volume of a rectangular solid is
V=Bh
can also be used to find the volume of a cylinder
Where,
“B” in the rectangular prism is the area of the rectangle
“B” in the cylinder is the area of the circle

Try It!

The area of the base of the cylinder is 78.5 in.2. What is the volume of the cylinder?
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 33
V = Bh
= _______ ∙ _______
= _______
The volume of the cylinder is ________ cubic inches.
Answer:
It is given that
The area of the base of the cylinder is 78.5 in.2
Now,
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 33
Now,
We know that,
The volume of a cylinder (V) = Bh
Where,
“B” is defined as the area of the circle
So,
V = 78.5 × 11
= 863.5 in.³
Hence, from the above,
We can conclude that the volume of the given cylinder is: 863.5 cubic inches

Convince Me!
Why can you use the formula V = Bh to find the volume of a cylinder?
Answer:
The representation of the cylinder is:

Now,
From the given figure,
We know that,
The two circles that are in the top and bottom positions are congruent
So,
The area for both the circles is also the same
Now,
We know that,
Volume = Area × Height
Now,
We know that,
Area of the circle = πr²
Hence,
The volume of the cylinder (V) = πr²h

Try It!

Lin is building a cylindrical planter with a base diameter of 15 inches. She has 5,000 cubic inches of soil to fill her planter. What is the height of the largest planter Lin can build? Use 3.14 for π, and round to the nearest inch.
Answer:
It is given that
Lin is building a cylindrical planter with a base diameter of 15 inches. She has 5,000 cubic inches of soil to fill her planter.
So,
From the given information,
The volume of the cylindrical planter = 5,000 cubic inches
The diameter of the cylindrical planter = 15 inches
Now,
We know that,
The volume of a cylinder (V) = πr²h
= \(\frac{πd²h}{4}\)
So,
5,000 = \(\frac{3.14 × 15 × 15 × h}{4}\)
5,000 = 176.625h
h = \(\frac{5,000}{176.625}\)
h = 28.3 inches
Hence, from the above,
We can conclude that the height of the largest planter Lin can build is: 28.3 inches

KEY CONCEPT
The formula for the volume of a cylinder is the same as the formula for the volume of a prism. The formula for the volume of a cylinder is V= Bh, where B is the area of the circular base and h is the height of the cylinder.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 34

Do You Understand?
Question 1.
Essential Question How is the volume of a cylinder related to the volume of a rectangular prism?
Answer:
Rectangular prisms and cylinders are somewhat similar because they both have two bases and a height.
The formula for the volume of a rectangular solid is
V=Bh
can also be used to find the volume of a cylinder
Where,
“B” in the rectangular prism is the area of the rectangle
“B” in the cylinder is the area of the circle

Question 2.
Use Structure What two measurements do you need to know to find the volume of a cylinder?
Answer:
We know that,
The volume of a cylinder (V) = πr²h
Now,
From the given formula,
We can observe that
π is a constant
Hence, from the above,
We can conclude that the two measurements that needed to be known are:
a. Radius of the cylinder
b. The height of the cylinder

Question 3.
Reasoning Cylinder A has a greater radius than Cylinder B. Does Cylinder A necessarily have a greater volume than Cylinder B? Explain.
Answer:
It is given that
Cylinder A has a greater radius than Cylinder B
Now,
We know that,
The volume of a cylinder (V) = πr²h
Now,
Fro the above,
We can observe that
Volume (V) ∝ Radius²
So,
When we increase the value of the radius, the value of the volume will automatically increase
Hence, from the above,
We can conclude that cylinder A has a greater volume than Cylinder B

Do You Know How?
Question 4.
What is the volume of the cylinder? Express your answer in terms of π.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 35
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 35
Now,
We know that,
The volume of a cylinder (V) = Bh
Where,
B = πr²
So,
V = 4π × 10
V = 40π mm³
Hence, from the above,
We can conclude that the volume of the given cylinder in terms of π is: 40π mm³

Question 5.
What is the approximate height of the cylinder? Use 3.14 for π, and if necessary, round to the nearest tenth.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 36
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 36
Now,
From the given figure,
We can observe that
The volume of a cylinder (V) = 314 ft³
The radius of a cylinder = 10 ft
Now,
We know that,
The volume of a cylinder (V) = πr²h
So,
314 = 3.14 × 10 × 10 × h
h = \(\frac{314}{3.14 × 10 × 10}\)
h = 1 ft
Hence, from the above,
We can conclude that the height of the given cylinder is: 1 ft

Question 6.
What is the volume of the cylinder? Use 3.14 for π, and if necessary, round to the nearest tenth.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 37
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 37
Now,
From the given figure,
We can observe that
The height of a cylinder = 4 cm
The circumference of a circle = 22.4 cm
Now,
We know that,
The circumference of a circle = 2πr
So,
2πr = 22.4
r = \(\frac{22.4}{2 × 3.14}\)
r = 3.56 cm
Now,
We know that,
The volume of a cylinder (V) = πr²h
So,
V = 3.14 × 3.56 × 3.56 × 4
= 159.2 cm³
Hence, from the above,
We can conclude that the volume of the given cylinder is: 159.2 cm³

Practice & Problem Solving

Question 7.
Leveled Practice What is the volume of a cylinder with a radius of 5 centimeters and height of 2.5 centimeters? Use 3.14 for π.
V = π ________ 2 ∙ ________
= π ______ ∙ ________
= _______ π
The volume of the cylinder is about _______ cubic centimeters.
Answer:
It is given that
The radius of a cylinder (r) = 5 cm
The height of a cylinder (h) = 2.5 cm
Now,
We know that,
The volume of a cylinder (V) = πr²h
So,
V = 3.14 × 5 × 5 × 2.5
= 196.25 cm
Hence, from the above,
We can conclude that the volume of the given cylinder is: 196.25 cm³ (or) 62.5π cm³

Question 8.
Find the volume of each cylinder in terms of. Which cylinder has the greater volume?
Cylinder A: Area of Base = 61 ft2, height = 10 ft
Cylinder B: Circumference = 6π ft, height = 6 ft
Answer:
The given data is:
Cylinder A: Area of Base = 61 ft2, height = 10 ft
Cylinder B: Circumference = 6π ft, height = 6 ft
Now,
We know that,
The volume of a cylinder (V) = Bh
Where,
B is the area of the circle
Now,
For Cylinder A:
V = 61 × 10
= 610 ft³
For Cylinder B:
We know that,
Circumference = 2πr
So,
2πr = 6π
r = \(\frac{6π}{2π}\)
= 3 ft
So,
V = 3.14 × 3 × 3 × 6
= 169.56 ft³
Hence, from the above,
We can conclude that Cylinder A has the greatest volume when we compare the volumes of Cylinder A and Cylinder B

Question 9.
The volume of a cylinder is 2251 cubic inches, and the height of the cylinder is 1 inch. What is the radius of the cylinder?
Answer:
It is given that
The volume of a cylinder is 2251 cubic inches, and the height of the cylinder is 1 inch
Now,
We know that,
The volume of a cylinder (V) = πr²h
So,
2251 = 3.14 × r² × 1
r² = \(\frac{2251}{3.14}\)
r² = 716.87 in²
r = 26.77 in
Hence, from the above,
We can conclude that the radius of the given cylinder is: 26.77 in.

Question 10.
A company is designing a new cylindrical water bottle. The volume of the bottle is 103 cubic centimeters. What is the radius of the water bottle? Estimate using 3.14 for π, and round to the nearest hundredth.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 38
Answer:
It is given that
A company is designing a new cylindrical water bottle. The volume of the bottle is 103 cubic centimeters
Now,
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 38
Now,
We know that,
The volume of a cylinder (V) = πr²h
So,
103 = 3.14 × r² × 8.1
r² = \(\frac{103}{3.14 × 8.1}\)
r² = 4.05cm²
r = 2.01 cm
Hence, from the above,
We can conclude that the radius of the given cylinder is: 2.01 cm

Question 11.
Use the figure at the right.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 39
a. Find the volume of the cylinder in terms of π.
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 39
Now,
From the given figure,
We can observe that
The radius of the cylinder (r) = 4 in.
The height of the cylinder (h) = 3 in
Now,
We know that,
The volume of a cylinder (V) = πr²h
So,
V = π × 4 × 4 × 3
V = 48π in.³
Hence, from the above,
We can conclude that the volume of the given cylinder in terms of π is: 48π in.³

b. Is the volume of a cylinder, which has the same radius but twice the height, greater or less than the original cylinder? Explain.
Answer:
From part (a),
The radius of the cylinder (r) = 4 in.
The height of the cylinder (h) = 3 in
So,
Now,
For part (b),
The radius of the cylinder (r) = 4 in.
The height of the cylinder (h) = 6 in.
So,
V = π × 4 × 4 × 6
= 96π in.³
Hence, from the above,
We can conclude that the volume of the cylinder we obtained in part (b) is greater than the volume of the cylinder we obtained in part (a)

Question 12.
Reasoning A rectangular piece of cardboard with dimensions 6 inches by 8 inches is used to make the curved side of a cylinder-shaped container. Using this cardboard, what is the greatest volume the cylinder can hold? Explain.
Answer:
It is given that
A rectangular piece of cardboard with dimensions 6 inches by 8 inches is used to make the curved side of a cylinder-shaped container.
Now,
Let the height of the cylinder be: 6 inches (or) 8 inches
Now,
We know that,
The volume of a rectangular prism (V) = Length × Width × Height
So,
For h = 6 inches:
V = 6 × 8 × 6
= 288 cubic inches
For h = 8 inches:
V = 6 × 8 × 8
= 384 cubic inches
Hence, from the above,
We can conclude that the greatest volume the given cylinder can hold is: 384 cubic inches

Question 13.
The cylinder shown has a volume of 885 cubic inches.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 40
a. What is the radius of the cylinder? Use 3.14 for π.
Answer:
It is given that
The cylinder shown has a volume of 885 cubic inches.
Now,
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 40
Now,
From the given figure,
We can observe that
The height of a cylinder (h) = 11.7 in.
Now,
We know that,
The volume of a cylinder (V) = πr²h
So,
885 = 3.14 × r² × 11.7
r² = \(\frac{885}{3.14 × 11.7}\)
r² = 24.08
r = 4.9 in.
Hence, from the above,
We can conclude that the radius of the given cylinder is: 4.9 in.

b. Reasoning If the height of the cylinder is changed, but the volume stays the same, then how will the radius change? Explain.
Answer:
We know that,
The volume of a cylinder (V) = πr²h
Now,
It is given that
Volume —–> Constant
Height —– > Changed
Now,
From the given formula,
If the volume is constant, then
h ∝ \(\frac{1}{r²}\)
Hence, from the above relation,
We can conclude that
If the value of height increases, then the value of radius decreases
If the value of height decreases, then the value of radius increases

Question 14.
Toy rubber balls are packaged in a cylinder that holds 3 balls. Find the volume of the cylinder. Use 3.14 for π, and round to the nearest tenth.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 41
Answer:
It is given that
Toy rubber balls are packaged in a cylinder that holds 3 balls
Now,
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 41
Now,
From the given figure,
We can observe that
The height of the cylinder (h) = 20.7 cm
The diameter of the cylinder (d) = 6.9 cm
Now,
We know that,
The volume of a cylinder (V) = πr²h
= \(\frac{πd²h}{4}\)
So,
V = \(\frac{3.14 × 20.7 × 20.7 × 6.9}{4}\)
= 2,321 cm³
Hence, from the above,
We can conclude that the volume of the given cylinder is: 2,321 cm³

Question 15.
Higher-Order Thinking
An insulated collar is made to cover a pipe. Find the volume of the material used to make the collar. Let r = 3 inches, R= 5 inches, and h = 21 inches. Use 3.14 for π, and round to the nearest hundredth.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 42
Answer:
It is given that
An insulated collar is made to cover a pipe.
Now,
The given data is:
r = 3 inches, R= 5 inches, and h = 21 inches
Now,
The radius of insulated collar = R – r
= 5 – 3
= 2 inches
Now,
The volume of a cylinder (V) = πr²h
So,
The volume of the material that is used to make the collar (V) = 3.14 × 2 × 2 × 21
= 263.76 cubic inches
Hence, from the above,
We can conclude that the volume of the material that is used to make the collar is: 263.76 cubic inches

Assessment Practice
Question 16.
The volume of a cylinder is 1,029π cubic centimeters. The height of the cylinder is 21 centimeters. What is the radius, to the nearest centimeter, of the cylinder?
Answer:
It is given that
The volume of a cylinder is 1,0291 cubic centimeters. The height of the cylinder is 21 centimeters.
Now,
We know that,
The volume of a cylinder (V) = πr²h
So,
1,029π = πr² × 21
r² = \(\frac{1,029}{21}\)
r² = 49
r = 7 cm
Hence, from the above,
We can conclude that the radius of the given cylinder is: 7 cm

Question 17.
The diameter of a cylinder is 7 yards. The height is 12 yards. What is the volume, in terms of π and to the nearest cubic yard, of the cylinder?
Answer:
It is given that
The diameter of a cylinder is 7 yards. The height is 12 yards
Now,
We know that,
The volume of a cylinder (V) = πr²h
= \(\frac{πd²h}{4}\)
So,
V = \(\frac{3.14 × 7 × 12 × 7}{4}\)
= 1,846.32 yards³ (or) 588π yards³
Hence, from the above,
We can conclude that the volume of the given cylinder is: 1,846.32 cubic yards (or) 588π cubic yards

Question 18.
A cylinder is shown. What statements about the cylinder are true?
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 43
☐ The radius of the cylinder is 2 ft.
☐ The diameter of the cylinder is 4 yd.
☐ The height of the cylinder is 8 in.
☐ The volume of the cylinder is 32 in.2.
☐ The volume of the cylinder is 32π in.3.
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 43
Now,
From the given figure,
We can observe that
The diameter of the cylinder = 4 in.
The height of the cylinder = 8 in.
So,
The radius of the cylinder = \(\frac{Diameter}{2}\)
= 2 in.
Now,
We know that,
The volume of a cylinder (V) = πr²h
So,
V = 3.14 × 2 × 2 × 8
= 32π in.³
= 100.48 in.³
Hence, from the above,
We can conclude that the statements that are true about the given cylinder are:

Topic 8 MID-TOPIC CHECKPOINT

Question 1.
Vocabulary Select all the statements that describe surface area and volume. Lessons 8-1 and 8-2
☐ Surface area is the sum of the areas of all the surfaces of a figure.
☐ Volume is the distance around a figure.
☐ The surface area is a three-dimensional measure.
☐ Volume is the amount of space a figure occupies.
☐ Volume is a three-dimensional measure.
Answer:
The above statements that describe the surface area and volume are:

In 2-4, use the figure at the right. Sallie packed a cone-shaped cup inside of a cylindrical package.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 44
Question 2.
The cone-shaped cup is made out of paper. How much paper was used to make the cup, excluding the opening at the top of the cup? Use 3.14 for π, and round to the nearest tenth. Lesson 8-1
Answer:
It is given that
Sallie packed a cone-shaped cup inside of a cylindrical package and the cone-shaped cup is made out of paper
Now,
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 44
Now,
From the given figure,
We can observe that
The slant height of cone (l) is: 33 cm
The diameter of the cone (d) is: 20 cm
So,
The radius of cone (r) = \(\frac{Diameter}{2}\)
= 10 cm
Now,
We know that,
The surface area of a cone (S.A) = πr² + πrl
So,
S.A = 3.14 × 10 × 10 + 3.14 × 10 × 33
= 314 + 1,036.2
= 1,350.2 cm²
Hence, from the above,
We can conclude that
We have to use 1,350.2 cm² of paper was used to make the cup, excluding the opening at the top of the cup

Question 3.
The cylindrical package is made out of cardboard. In terms of π, how much cardboard was used to make the package? Lesson 8-1
Answer:
It is given that the cylindrical package is made out of cardboard
Now,
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 44
Now,
From the given figure,
We can observe that
The height of the cylinder (h) is: 33 cm
The diameter of the cylinder (d) is: 20 cm
So,
Radius = \(\frac{Diameter}{2}\)
= \(\frac{20}{2}\)
= 10 cm
Now,
We know that,
The surface area of a cylinder (S.A) = 2πr² + 2πrh
So,
S.A = 2π × 10² + 2π × 10 × 33
= 200π + 660π
= 860π cm²
Hence, from the above,
We can conclude that 860π cm² of cardboard was used to make the package

Question 4.
How much space does the package occupy in terms of π? Lesson 8-1
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 44
Now,
From the above,
We can observe that the given figure is a cylinder
Now,
From the given figure,
We can observe that
The height of the cylinder (h) is: 33 cm
The diameter of the cylinder (d) is: 20 cm
So,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{20}{2}\)
r = 10 cm
Now,
We know that,
The volume of a cylinder (V) = πr²h
So,
V = π × 10² × 33
= 3,300π cm³
Hence, from the above,
We can conclude that 3,300π cm³ of space does the package occupy in terms of π

Question 5.
What is the surface area of the sphere in terms of π? Lesson 8-1
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 45
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 45
Now,
From the given figure,
We can observe that
The radius of the sphere (r) is: 3 ft
Now,
We know that,
The surface area of a sphere (S.A) = 4πr²
So,
S.A = 4π × 3²
= 36π ft²
Hence, from the above,
We can conclude that the surface area of the given sphere is: 36π ft²

Question 6.
The volume of the cylinder is 400π cm3. What is the height of the cylinder? Lesson 8-2
A. 5 cm
B. 16 cm
C. 25 cm
D. 80 cm
Answer:
It is given that
The volume of the cylinder is 400π cm³
Now,
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 45
Now,
From the given figure,
We can observe that
The diameter of the cylinder (d) is: 10 cm
So,
Radius = \(\frac{Diameter}{2}\)
= \(\frac{10}{2}\)
= 5 cm
Now,
We know that,
The volume of a cylinder (V) = πr²h
So,
400π = π × 5² × h
h = \(\frac{400}{25}\)
h = 16 cm
Hence, from the above,
We can conclude that the volume of the given cylinder is: 16 cm

Topic 8 MID-TOPIC PERFORMANCE TASK

Melissa designed a sculpture in which a cylinder-shaped section was removed from a cube.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 46

PART A
Before painting the surface of the sculpture, Melissa wants to sand the surface where the cylinder section was removed. What is the surface area of the section she will sand? Use 3.14 for π. Explain how you found the surface area.
Answer:
It is given that
Melissa designed a sculpture in which a cylinder-shaped section was removed from a cube.
Now,
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 46Now,
From the given figure,
The diameter of the cylinder (d) is: 5 cm
The height of the cylinder (d) is: 10 cm
So,
The radius of the cylinder (r) = \(\frac{Diameter of the cylinder}{2}\)
r = 2.5 cm
Now,
We know that,
We know that,
The surface area of a cylinder (S.A) = 2πr² + 2πrh
So,
S.A = 2 × 3.14 × 2.5 × 2.5 + 2 × 3.14 × 2.5 × 10
= 39.25 + 157
= 196.25 cm²
Hence, from the above,
We can conclude that 196.25 cm²  is the surface area of the section Melissa will sand

PART B
Melissa has a can of spray paint that covers about 6,500 square centimeters. Can Melissa apply two coats of paint to the entire sculpture? Explain. Use 3.14 for π.
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 46
Now,
From the above,
We can observe that
The scripture is the combination of the cube and the cylinder
Now,
We know that,
The surface area of a cube (S.A) = 6a²
Where,
a is the side of the cube
So,
S.A of the cube = 6 × 10²
= 600 cm²
Now,
From part (a),
The S.A of the cylinder = 196.25 cm²
So,
The S.A of the scripture = 600 + 196.25
= 796.25 cm²
So,
6,500 > 796.25 × 2
Hence, from the above,
We can conclude that Melissa can apply two coats of paint to the entire sculpture

PART C
What is the volume of the sculpture? Use 3.14 for π.
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 46
Now,
From the above,
We can observe that
The scripture is the combination of the cube and the cylinder
Now,
The diameter of the cylinder (d) is: 5 cm
The height of the cylinder (h) is: 10 cm
So,
The radius of the cylinder (r) is: 2.5 cm
Now,
We know that,
The volume of the cylinder (V) = πr²h
The volume of the cube (V) = a³
Where,
a is the side of the cube
So,
The volume of the scripture (V) = πr²h + a³
So,
V = 3.14 × 2.5 × 2.5 × 10 + 10³
= 196.25 + 1,000
= 1,196.25 cm³
Hence, from the above,
We can conclude that the volume of the scripture is: 1,196.25 cm³

Lesson 8.3 Find Volume of Cones

Solve & Discuss It!
A landscape architect uses molds for casting rectangular pyramids and rectangular prisms to make garden statues. He plans to place each finished pyramid on top of a prism. If one batch of concrete mix makes one prism or three pyramids, how does the volume of one pyramid compare to the volume of one prism? Explain.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 47
I can… find the volume of cones.
Answer:
It is given that
A landscape architect uses molds for casting rectangular pyramids and rectangular prisms to make garden statues. He plans to place each finished pyramid on top of a prism and one batch of concrete mix makes one prism or three pyramids
Now,
We know that,
The prism is in the shape of the cylinder
The pyramid is in the shape of the cone
Now,
We know that,
The volume of a prism (V) = πr²h
The volume of a pyramid (V) = \(\frac{1}{3}\)πr²h
So,
The volume of a prism = 3 × The volume of a pyramid
Hence, from the above,
We can conclude that
The volume of a prism is 3 times the volume of a pyramid

Look for Relationships
What do you notice about the dimensions of the bases of the pyramid and prism? How are the heights of the two solids related?
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 47
Now,
From the given figure,
We can observe that
a. The dimensions of the bases of the prism and the pyramid are the same
b. The heights of the pyramid and the prism are the same

Focus on math practices
Make Sense and Persevere If the architect mixes 10 batches of concrete, how many sculptures combining 1 prism and 1 pyramid could he make? Explain.
Answer:
It is given that
one batch of concrete mix makes one prism or three pyramids
So,
The ratio of the mix of prism and pyramid in 1 batch is: 1 : 3
Hence,
For 10 batches of the mix of concrete,
We can make sculptures combining 1 prism and 1pyramid are: 10 prisms and 30 pyramids

Essential Question
How is the volume of a cone related to the volume of a cylinder?
Answer:
The volumes of a cone and a cylinder are related in the same way as the volumes of a pyramid and a prism is related. If the heights of a cone and a cylinder are equal, then the volume of the cylinder is 3 times as much as the volume of a cone

Try It!
Find the volume of the cone. Use 3.14 for π.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 48
The volume of the cone is about ________ cubic inches.
V = ____ πr²h
≈ _______(3.14) (______)2 (4)
= ________ (3.14) (______)(4)
= _________
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 48
From the above figure,
We can observe that
The radius of the cone (r) is 1.5 in.
The height of the cone (h) is 4 in.
Now,
We know that,
The volume of the cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × 3.14 × (1.5)² × 4
= 9.42 in.³
Hence, from the above,
We can conclude that the volume of the given cone is: 9.42 in.³

Convince Me!
If you know the volume of a cone, how can you find the volume of a cylinder that has the same height and radius as the cone?
Answer:
We know that,
If the cylinder and the cone has the same height and radius, then
The volume of cone = \(\frac{1}{3}\) × The volume of cylinder

Try It!

Find the volume of each cone.
a. Use \(\frac{22}{7}\) for π. Express the answer as a fraction.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 49
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 49
Now,
From the given figure,
We can observe that
The slant height (l) is: 5 mm
The height of the cone (h) is: 3 mm
Now,
We know that,
l² = r²+ h²
So,
5² = r² + 3²
r² = 25 – 9
r² = 16
r = 4 mm
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × \(\frac{22}{7}\) × 4² × 3
= \(\frac{1,056}{21}\) mm³
Hence, from the above,
We can conclude that the volume of the given cone in the fraction form is: \(\frac{1,056}{66}\) mm³

b. Express the volume in terms of π.
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 50
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 50
From the given figure,
We can observe that
The height of the cone (h) is: 21 ft
The circumference of the circle (C) is: 16π ft
Now,
We know that,
The circumference of the circle (C) = 2πr
So,
2πr = 16π
r = 8 ft
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × π × 8² × 21
= 448π ft³
Hence, from the above,
We can conclude that the volume of the given cone in terms of π is: 448π ft³

KEY CONCEPT

The volume of a cone is \(\frac{1}{3}\) the volume of a cylinder with the same base and height. The formula for the volume of a cone is V = \(\frac{1}{3}\)Bh, where B is the area of the base and his the height of the cone.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 51

Do You Understand?
Question 1.
Essential Question How is the volume of a cone related to the volume of a cylinder?
Answer:
The volumes of a cone and a cylinder are related in the same way as the volumes of a pyramid and a prism is related. If the heights of a cone and a cylinder are equal, then the volume of the cylinder is 3 times as much as the volume of a cone

Question 2.
Use Structure What dimensions do you need to find the volume of a cone?
Answer:
To find the volume of a cone,
The dimensions we need are:
a. The radius of the cone
b. The height of the cone

Question 3.
Look for Relationships If you know a cone’s radius and slant height, what must you do before you can find its volume?
Answer:
If you know a cone’s radius (r) and slant height(l), then
The volume of a cone (V) is given as:
V = \(\frac{1}{3}\)πr² × \(\sqrt{l² – r²}\)

Do You Know How?
Question 4.
Wanda found a cone-shaped seashell on the beach. The shell has a height of 63 millimeters and a base radius of 8 millimeters. What is the volume of the seashell? Estimate 63 mm using \(\frac{22}{7}\) for π.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 52
Answer:
It is given that
Wanda found a cone-shaped seashell on the beach. The shell has a height of 63 millimeters and a base radius of 8 millimeters
Now,
The given figure is:
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 52
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × \(\frac{22}{7}\) × 8² × 63
= 4,224 mm³
Hence, from the above,
We can conclude that the volume of the seashell is: 4,224 mm³

Question 5.
What is the volume of the cone? Estimate using 3.14 for π, and round to the nearest tenth.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 53
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 53
Now,
From the given figure,
We can observe that
The height of the cone (h) is: 40mm
The slant height of the cone (l) is: 41 mm
Now,
We know that,
l² = r² + h²
So,
41² = r²+ 40²
r² = 81
r = 9 mm
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × 3.14 × 9² × 40
= 3,391.2 mm³
Hence, from the above,
We can conclude that the volume of the given cone is: 3,391.2 mm³

Question 6.
What is the volume of the cone in terms of π if the circumference of the base is 1.4π feet?
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 54
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 54
Now,
From the given figure,
We can observe that
The height of the cone (h) is: 2.7 ft
Now,
We know that,
Circumference (C) = 2πr
So,
2πr = 1.4π
r = 0.7 ft
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × π × (0.7)² × 2.7
= 0.441π ft³
Hence, from the above,
We can conclude that the volume of the given cone is: 0.441π ft³

Practice & Problem Solving

Multimedia Leveled Practice In 7 and 8, find the volumes of the cones.
Question 7.
What is the volume of the cone? Write your answer in terms of π.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 55
Answer:
From the given figure,
We can observe that
The radius of the cone (r) is: 3 cm
The height of the cone (h) is: 4 cm
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × π × 3² × 4
= 12π cm³
Hence, from the above,
We can conclude that the volume of the given cone is: 12π cm³

Question 8.
What is the volume of the cone to the nearest hundredth? Use 3.14 for π.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 56
Answer:
From the given figure,
We can observe that
The radius of the cone (r) is: 16 units
The height of the cone (h) is: 36 units
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × 3.14 × 16² × 36
= 9,646.08 units³
Hence, from the above,
We can conclude that the volume of the given cone is: 9,646.08 units³

Question 9.
If a cone-shaped hole is 3 feet deep and the circumference of the base of the hole is 44 feet, what is the volume of the hole? Use \(\frac{22}{7}\) for π.
Answer:
It is given that
A cone-shaped hole is 3 feet deep and the circumference of the base of the hole is 44 feet
Now,
We know that,
Circumference (C) = 2πr
So,
2πr = 44
r = \(\frac{44}{2π}\)
r = 7 feet
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × \(\frac{22}{7}\) × 7² × 3
= 154 feet³
Hence, from the above,
We can conclude that the volume of the given cone-shaped hole is: 154 feet³

Question 10.
The volume of the cone is 462 cubic yards. What is the radius of the cone? Use \(\frac{22}{7}\) for π.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 57
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 57
Now,
From the given figure,
We can observe that
The height of the cone (h) is: 9 yd
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
462 = \(\frac{1}{3}\) × \(\frac{22}{7}\) × r² × 9
r² = \(\frac{462}{9.428}\)
r = 7 yd
Hence, from the above,
We can conclude that the radius of the given cone is: 7 yd

Question 11.
A city engineer determines that 5,500 cubic meters of sand will be needed to combat erosion at the city’s beach. Does the city have enough sand to combat erosion? Use \(\frac{22}{7}\) for π. Explain.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 58
Answer:
It is given that
A city engineer determines that 5,500 cubic meters of sand will be needed to combat erosion at the city’s beach.
Now,
The given figure is:
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 58
Now,
From the given figure,
We can observe that
The slant height of the cone(l) is: 37 m
The height of the cone (h) is: 35 m
Now,
We know that,
l² = r²+ h²
37² = r² + 35²
r² = 37² – 35²
r = 12 m
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × \(\frac{22}{7}\) × 12² × 35
= 5,280 m³
So,
5,500 > 5,280
Hence, from the above,
We can conclude that the city has enough sand to combat erosion

Question 12.
A water tank is shaped like the cone shown.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 59
a. How much water can the tank hold? Use 3.14 for π, and round to the nearest tenth.
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 59
Now,
From the given figure,
We can observe that
The slant height of the cone (l) is: 61 ft
The height of the cone (h) is: 60 ft
Now,
We know that,
l² = r²+ h²
61² = r² + 60²
r² = 61² – 60²
r = 11 ft
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × 3.14 × 11² × 60
= 7,598.8 ft³
Hence, from the above,
We can conclude that the amount of water that the tank can hold is: 7,598.8 ft³

b. If water is drained from the tank to fill smaller tanks that each hold 500 cubic feet of water, how many smaller tanks can be filled?
Answer:
It is given that the water is drained from the tank to fill smaller tanks that each holds 500 cubic feet of water
Now,
From part (a),
We know that,
The amount of water that the tank can hold is: 7,598.8 ft³
Now,
The number of smaller tanks that can be filled = \(\frac{The amount of water that the tank can hold}{The amount of water that the smaller tank can hold}\)
= \(\frac{7,598.8}{500}\)
≅ 15
Hence, from the above,
We can conclude that the number of smaller tanks that can be filled is: 15

Question 13.
An ice cream cone is filled exactly level with the top of a cone. The cone has a 9-centimeter depth and a base with a circumference of 91 centimeters. How much ice cream is in the cone in terms of π?
Answer:
It is given that
An ice cream cone is filled exactly level with the top of a cone. The cone has a 9-centimeter depth and a base with a circumference of 91 centimeters
Now,
We know that,
Circumference (C) = 2πr
So,
2πr = 91
r = \(\frac{91}{2π}\)
r = 14.49 cm
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × π × (14.49)² × 9
= 629.88π cm³
Hence, from the above,
We can conclude that the amount of ice cream that is in the cone in terms of π is: 629.88π cm³

Question 14.
In the scale model of a park, small green cones represent trees. What is the volume of one green cone? Use \(\frac{22}{7}\) for π.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 60
Answer:
The given green cone is:
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 60
Now,
From the given green cone,
We can observe that
The slant height of the cone (l) is: 65 mm
The height of the cone (h) is: 63 mm
Now,
We know that,
l² = r²+ h²
65² = r² + 603²
r² = 65² – 63²
r = 16 mm
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × \(\frac{22}{7}\) × 16² × 63
= 16,896 mm³
Hence, from the above,
We can conclude that the volume of one green cone is: 16,896 mm³

Question 15.
Reasoning Compare the volumes of two cones. One has a radius of 5 feet and a slant height of 13 feet. The other one has a height of 5 feet and a slant height of 13 feet.
a. Which cone has the greater volume?
Answer:
The given data is:
Cone 1: Radius: 5 feet       Slant height: 13 feet
Cone 2: Height: 5 feet       Slant height: 13 feet
Now,
We know that,
l² = r²+ h²
So,
For cone 1:
13² = h² + 5²
h² = 13² – 5²
h = 12 feet
For cone 2:
13² = r² + 5²
r² = 13² – 5²
r = 12 feet
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
For Cone 1:
V = \(\frac{1}{3}\) × \(\frac{22}{7}\) × 5² × 12
= 314.28 feet³
For Cone 2:
V = \(\frac{1}{3}\) × \(\frac{22}{7}\) × 12² × 5
= 754.28 feet³
Hence, from the above,
We can conclude that Cone 2 has the greater volume

b. What is the volume of the larger cone in terms of π?
Answer:
From part (a),
We can observe that,
Cone 2 has a greater volume
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × π × 12² × 5
= 240π feet³

Question 16.
An artist makes a cone-shaped sculpture for an art exhibit. If the sculpture is 7 feet tall and has a base with a circumference of 24.492 feet, what is the volume of the sculpture? Use 3.14 for π, and round to the nearest hundredth.
Answer:
It is given that
An artist makes a cone-shaped sculpture for an art exhibit and the sculpture is 7 feet tall and has a base with a circumference of 24.492 feet
Now,
We know that,
Circumference (C) = 2πr
So,
2πr = 24.492
r = \(\frac{24.492}{2π}\)
r = 3.9 feet
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × 3.14 × 3.9² × 7
= 111.43 feet³
Hence, from the above,
We can conclude that the volume of the given cone-shaped sculpture is: 111.43 feet³

Question 17.
Higher-Order Thinking A cone has a radius of 3 and a height of 11.
a. Suppose the radius is increased by 4 times its original measure. How many times greater is the volume of the larger cone than the smaller cone?
Answer:
It is given that
A cone has a radius of 3 and a height of 11
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × 3.14 × 3² × 11
= 103.62 units³
Now,
If the radius is increased by 4 times of its original measure, then
V = \(\frac{1}{3}\) × 3.14 × (3 × 4)² × 11
= 1,657.92 units³
Now,
The number of times the volume of the larger cone than the smaller cone = \(\frac{1,657.92}{103.62}\)
= 16
Hence, from the above,
We can conclude that the volume of the larger cone is 16 times greater than the volume of the smaller cone

b. How would the volume of the cone change if the radius were divided by four?
Answer:
From part (a),
We know that,
The volume of the cone with a radius of 3 and a height of 11 units is: 103.62 units³
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × 3.14 × (3 ÷ 4)² × 11
= 6.476 units³
Now,
The ratio of the volume of the changed cone to the volume of the original cone = \(\frac{6.476}{103.62}\)
= 0.06
Hence, from the above,
We can conclude that the volume of the cone will be 0.06 times of the original cone

Assessment Practice
Question 18.
List the cones described below in order from least volume to greatest volume.
• Cone 1: radius 6 cm and height 12 cm
• Cone 2: radius 12 cm and height 6 cm
• Cone 3: radius 9 cm and height 8 cm
A. Cone 2, Cone 3, Cone 1
B. Cone 1, Cone 3, Cone 2
C. Cone 2, Cone 1, Cone 3
D. Cone 1, Cone 2, Cone 3
Answer:
The given data is:
a. Cone 1: radius 6 cm and height 12 cm
b. Cone 2: radius 12 cm and height 6 cm
c.  Cone 3: radius 9 cm and height 8 cm
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
For Cone 1:
V = \(\frac{1}{3}\) × 3.14 × 6² × 12
= 452.16 cm³
For Cone 2:
V = \(\frac{1}{3}\) × 3.14 × 12² × 6
= 904.32 cm³
For Cone 3:
V = \(\frac{1}{3}\) × 3.14 × 9² × 8
= 678.24 cm³
Hence, from the above,
We can conclude that the order of the volumes from the least to the greatest is:
Cone 1 < Cone 3 < Cone 2

Question 19.
What is the volume, in cubic inches, of a cone that has a radius of 8 inches and a height of 12 inches? Use 3.14 for π, and round to the nearest hundredth.
Answer:
It is given that
A cone has a radius of 8 inches and a height of 12 inches
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × 3.14 × 8² × 12
= 803.84 inches³
Hence, from the above,
We can conclude that the volume of the given cone is: 803.84 inches³

Lesson 8.4 Find Volume of Spheres

Explore It!
Marshall uses the beaker to fill the bowl with water.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 61
I can… find the volume of a sphere and use it to solve problems.

A. Draw and label three-dimensional figures to represent the beaker and the bowl.
Answer:
The representation of the three-dimensional figures that represent the beaker and bowl are:

B. Marshall has to fill the beaker twice to completely fill the bowl with water. How can you use an equation to represent the volume of the bowl?
Answer:
The given figures are:
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 61
Now,
It is given that
Marshall has to fill the beaker twice to completely fill the bowl with water
Now,
From part (a),
We can observe that the beaker is in the form of a cone
Now,
We know that,
The volume of a cone = \(\frac{1}{3}\)πr²h
Now,
According to the given situation,
The volume of the bowl(V’) = 2 × The volume of the beaker(V)
V’ = 2 × \(\frac{1}{3}\)πr²h
Now,
From the given figures,
We can observe that
The height of a bowl is 2 times its radius
So,
V’ = \(\frac{2}{3}\)πr² (2r)
V’ = \(\frac{4}{3}\)πr³
Hence, from the above,
We can conclude that the volume of the bowl is: \(\frac{4}{3}\)πr³

Focus on math practices
Reasoning How is the volume of a sphere and the volume of a cone related? What must be true about the radius and height measurements for these relationships to be valid?
Answer:
We know that,
The relationship between the volume of the sphere and the volume of the cone is:
The volume of the sphere = 2 × The volume of the cone
Now,
For the above relationship to be valid,
a. The heights of the sphere and the cone must be the same
b. The radius of the sphere and the cone must be the same

Essential Question
How is the volume of a sphere related to the volume of a cone?
Answer:
The volume of a sphere is twice the volume of a cone that has the same circular base and height. i.e.,
The volume of the sphere = 2 × The volume of the cone

Try It!

What is the volume of a ball with a diameter of 6 centimeters? Use 3.14 for π.
V = \(\frac{4}{3}\) πr3
= \(\frac{4}{3}\) π _______3
≈ ________ ∙ ________
= __________
The volume of the ball is about _______ cm3
Answer:
It is given that
The diameter of a ball is: 6 cm
Now,
We know that,
The ball is in the form of a sphere
Now,
We know that,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{6}{2}\)
r = 3 cm
Now,
We know that,
The volume of a sphere (V) = \(\frac{4}{3}\)πr³
So,
V = \(\frac{4}{3}\) × 3.14 × 3³
= 113.04 cm³
Hence, from the above,
We can conclude that the volume of the given ball is about 113.04 cm³

Convince Me!
How is the volume of a sphere related to the volume of a cone that has the same circular base and height?
Answer:
The relationship between the volume of a cone and the volume of a sphere that has the same circular base and height is:
The volume of the sphere = 2 × The volume of the cone

Try It!

What is the volume of the composite figure shown? Use 3.14 for π.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 62
Answer:
The given composite figure is:
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 62
Now,
We know that,
A composite figure is made up of 2 or more two-dimensional figures
Now,
The given composite figure is made up of Hemisphere and Cone
Now,
We know that,
The volume of the given composite figure = The volume of the Hemisphere + The volume of the cone
Now,
From the given composite figure,
We can observe that
Radius (r) = 2 in.
Height (h) = 6 in.
Now,
We know that,
The volume of the Hemisphere (V) = \(\frac{2}{3}\)πr³
So,
V = \(\frac{2}{3}\) × 3.14 × 2³
= 16.74 in.³
Now,
We know that,
The volume of the cone (V’) = \(\frac{1}{3}\)πr²h
So,
V’ = \(\frac{1}{3}\) × 3.14 × 2² × 6
= 25.12 in.³
So,
The volume of the given composite figure = 16.74 + 25.12
= 41.84 in.³
Hence, from the above,
We can conclude that the volume of the given composite figure is: 41.84 in.³

KEY CONCEPT

The volume of a sphere is twice the volume of a cone that has the same circular base and height. The formula for the volume of a sphere with radius r is V = \(\frac{4}{3}\) πr3.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 63

Do You Understand?
Question 1.
Essential Question How is the volume of a sphere related to the volume of a cone?
Answer:
The volume of a sphere is twice the volume of a cone that has the same circular base and height. i.e.,
The volume of the sphere = 2 × The volume of the cone

Question 2.
Critique Reasoning Kristy incorrectly says that the volume of the sphere below is 144π cubic units. What mistake might Kristy have made?
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 64
Answer:
The given sphere is:
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 64
Now,
It is given that
Kristy incorrectly says that the volume of the sphere below is 144π cubic units
Now,
From the given sphere,
We can observe that
Radius (r) = 6 units
Now,
We know that,
The volume of a spher (V) = \(\frac{4}{3}\)πr³
So,
V = \(\frac{4}{3}\) × π × 6³
= 288π units³
Hence, from the above,
We can conclude that the mistake done by Kristy is:
Considering the sphere as the hemisphere and calculated the volume of the hemisphere instead of the sphere

Question 3.
Generalize Mehnaj has a set of blocks that are all the same height. The cone-shaped block has a volume of 125 cubic inches. The sphere-shaped block has a volume of 250 cubic inches. What do you know about the radius of the base of the cone-shaped block? Explain.
Answer:
It is given that
Mehnaj has a set of blocks that are all the same height. The cone-shaped block has a volume of 125 cubic inches. The sphere-shaped block has a volume of 250 cubic inches
So,
From the given situation,
We can observe that
a. The heights of the two cone-shaped blocks are the same
b. The volumes of the two cone-shaped blocks are different
Now,
We know that,
The volume of a cone = \(\frac{1}{3}\)πr²h
So,
V1 = \(\frac{1}{3}\)πr1²h1
V2 = \(\frac{1}{3}\)πr2²h2
So,
V1/V2 = r1²/ r2²
r1²/ r2² = \(\frac{125}{250}\)
r1² / r2² = 0.5
r1 / r2 = 0.707
Hence, from the above,
We can conclude that the radius of the first cone-based block is 0.707 times the radius of the second cone-shaped block

Do You Know How?
Question 4.
Clarissa has a decorative bulb in the shape of a sphere. If it has a radius of 3 inches, what is its volume? Use 3.14 for π.
Answer:
It is given that
Clarissa has a decorative bulb in the shape of a sphere and it has a radius of 3 inches
Now,
We know that,
The volume of a sphere (V) = \(\frac{4}{3}\)πr³
So,
V = \(\frac{4}{3}\) × 3.14 × 3³
= 113.04 inches³
Hence, from the above,
We can conclude that the volume of the given decorative bulb is: 113.04 inches³

Question 5.
A sphere has a surface area of about 803.84 square centimeters. What is the volume of the sphere? Use 3.14 for π and round to the nearest whole number.
Answer:
It is given that
A sphere has a surface area of about 803.84 square centimeters
Now,
We know that,
The surface area of a sphere (S.A) = 4πr²
So,
4πr² = 803.84
r² = \(\frac{803.84}{4π}\)
r² = 64
r = 8 cm
Now,
We know that,
The volume of a sphere (V) = \(\frac{4}{3}\)πr³
So,
V = \(\frac{4}{3}\) × 3.14 × 8³
= 2,143.57 cm³
≈2,144 cm³
Hence, from the above,
We can conclude that the volume of the given sphere is about 2,144 cm³

Question 6.
A water pipe is a cylinder 30 inches long, with a radius of 1 inch. At one end of the cylinder, there is a hemisphere. What is the volume of the water pipe? Explain.
Answer:
It is given that
A water pipe is a cylinder 30 inches long, with a radius of 1 inch. At one end of the cylinder, there is a hemisphere.
So,
The volume of the water pipe = The volume of the cylinder + The volume of the hemisphere
Now,
From the given water pipe,
We can observe that
Radius (r) = 1 in.
Height (h) = 30 in.
Now,
We know that,
The volume of the Hemisphere (V) = \(\frac{2}{3}\)πr³
So,
V = \(\frac{2}{3}\) × 3.14 × 1³
= 2.09 in.³
Now,
We know that,
The volume of the cylinder (V’) = πr²h
So,
V’ = 3.14 × 1² × 30
= 94.2 in.³
So,
The volume of the given water pipe = 2.09 + 94.2
= 96.29 in.³
Hence, from the above,
We can conclude that the volume of the given water pipe is: 96.29 in.³

Practice & Problem Solving

Question 7.
Leveled Practice What is the amount of air, in cubic centimeters, needed to fill the stability ball? Use 3.14 for π, and round to the nearest whole number. Use the formula
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 65
The volume of the stability ball is approximately __________ cubic centimeters.
Answer:
From the given figure,
We can observe that
The stability ball is in the form of a sphere
Now,
The diameter of the stability ball (d) is: 55 cm
Now,
We know that,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{55}{2}\)
r = 27.5 cm
Now,
We know that,
The volume of a sphere (V) = \(\frac{4}{3}\)πr³
So,
V = \(\frac{4}{3}\) × 3.14 × (27.5)³
= 87,069.53 cm³
≈87,070 cm³
Hence, from the above,
We can conclude that the volume of the stability ball is approximately 87,070 cm³

Question 8.
The spherical balloon has a 22-inch. diameter when it is fully inflated. Half of the air is let out of the balloon. Assume that the balloon remains a sphere. Keep all answers in terms of π.
a. Find the volume of the fully-inflated balloon.
Answer:
It is given that
The spherical balloon has a 22-inch. diameter when it is fully inflated. Half of the air is let out of the balloon.
Now,
From the given situation,
The diameter of the fully inflated balloon (d) is: 22 inches
Now,
We know that,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{22}{2}\)
r = 11 cm
Now,
We know that,
The volume of a sphere (V) = \(\frac{4}{3}\)πr³
So,
V = \(\frac{4}{3}\) × π × 11³
= 1,774.6π cm³
Hence, from the above,
We can conclude that the volume of the fully inflated balloon is: 1,774.6π cm³

b. Find the volume of the half-inflated balloon.
Answer:
It is given that
The spherical balloon has a 22-inch. diameter when it is fully inflated. Half of the air is let out of the balloon.
So,
The diameter of half-inflated balloon (d) = \(\frac{The diameter of fully inflated balloon}{2}\)
d = \(\frac{22}{2}\)
d = 11 cm
Now,
We know that,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{11}{2}\)
r = 5.5 cm
Now,
We know that,
The volume of a sphere (V) = \(\frac{4}{3}\)πr³
So,
V = \(\frac{4}{3}\) × π × (5.5)³
= 221.8π cm³
Hence, from the above,
We can conclude that the volume of the half-inflated balloon is: 221.8π cm³

c. What is the radius of the half-inflated balloon? Round to the nearest tenth.
Answer:
From part (b),
We can observe that
The diameter of half-inflated balloon (d) = \(\frac{The diameter of fully inflated balloon}{2}\)
d = \(\frac{22}{2}\)
d = 11 cm
Now,
We know that,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{11}{2}\)
r = 5.5 cm
Hence, from the above,
We can conclude that the radius of the half-inflated balloon is: 5.5 cm

Question 9.
Find the volume of the figure. Use 3.14 for π, and round to the nearest whole number.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 66
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 66
Now,
From the given figure,
We can observe that
The figure is a combination of a hemisphere and a cone
So,
From the given figure,
Diameter (d) =14 cm
Height (h) = 17 cm
Now,
We know that,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{14}{2}\)
r = 7 cm
Now,
We know that,
The volume of the figure (V) = The volume of a hemisphere + The volume of a cone
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × 3.14 × 7² × 17
= 871.87 cm³
Now,
We know that,
The volume of a hemisphere (V’) = \(\frac{2}{3}\)πr³
So,
V’ = \(\frac{2}{3}\) × 3.14 × 7³
= 718.01 cm³
So,
The volume of the given figure = 871.87 + 718.01
= 1,589.88 cm³
≈1,590 cm³
Hence, from the above,
We can conclude that the volume of the given figure is: 1,590 cm³

Question 10.
The surface area of a sphere is about 2,826 square millimeters. What is the volume of the sphere? Use 3.14 for π, and round to the nearest whole number.
Answer:
It is given that
The surface area of a sphere is about 2,826 square millimeters
Now,
We know that,
The surface area of a sphere (S.A) = 4πr²
So,
4πr² = 2,826
r² = \(\frac{2,826}{4π}\)
r² = 225
r = 15 mm
Now,
We know that,
The volume of a sphere (V) = \(\frac{4}{3}\)πr³
So,
V = \(\frac{4}{3}\) × 3.14 × 15³
= 14,130 mm³
Hence, from the above,
We can conclude that the volume of the given sphere is: 14,130 mm³

Question 11.
A sphere has a volume of 1,837.35 cubic centimeters. What is the radius of the sphere? Use 3.14 for π, and round to the nearest tenth.
Answer:
It is given that
A sphere has a volume of 1,837.35 cubic centimeters
Now,
We know that,
The volume of a sphere (V) = \(\frac{4}{3}\)πr³
So,
1,837.35 = \(\frac{4}{3}\)πr³
πr³ = \(\frac{1,837.35 × 3}{4}\)
πr³ = 1,378.01
r³ = \(\frac{1,378.01}{π}\)
r³ = 438.85
r = 0.333 cm
Hence, from the above,
We can conclude that the radius of the given sphere is: 0.333 cm

Question 12.
Find the volume of the solid. Use 3.14 for π, and round to the nearest whole number.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 67
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 67
From the above,
We can observe that the given figure is a composite figure
Now,
From the given figure,
We can observe that
Radius (r) = 4 m
Height (h) = 17 m
Now,
We know that,
The volume of the given figure = The volume of a hemisphere + The volume of a cylinder
Now,
We know that,
The volume of the Hemisphere (V) = \(\frac{2}{3}\)πr³
So,
V = \(\frac{2}{3}\) × 3.14 × 4³
= 133.97 m³
Now,
We know that,
The volume of the cylinder (V’) = πr²h
So,
V’ = 3.14 × 4² × 17
= 854.08 m³
So,
The volume of the given figure = 133.9 + 854.08
= 987.98 m³
Hence, from the above,
We can conclude that the volume of the given figure is: 987.98 m³

Question 13.
Your friend says that the volume of a sphere with a diameter of 3.4 meters is 164.55 cubic meters. What mistake might your friend have made? Find the correct volume. Use 3.14 for π and round to the nearest hundredth.
Answer:
It is given that
Your friend says that the volume of a sphere with a diameter of 3.4 meters is 164.55 cubic meters
Now,
From the given information,
Diameter (d) = 3.4 m
Now,
We know that,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{3.4}{2}\)
r = 1.7 m
Now,
We know that,
The volume of a sphere (V) = \(\frac{4}{3}\)πr³
So,
V = \(\frac{4}{3}\) × 3.14 × (1.7)³
= 20.56 m³
Hence, from the above,
We can conclude that
The mistake made by your friend is:
Consideration of diameter as radius and find the volume of the given sphere

Question 14.
A solid figure has a cone and hemisphere hollowed out of it. What is the volume of the remaining part of the solid? Use 3.14 for π, and round to the nearest whole number.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 68
Answer:
It is given that
A solid figure has a cone and hemisphere hollowed out of it
So,
The volume of the remaining part of the solid = | The volume of a hemisphere – The volume of a cone |
Now,
From the given solid,
We can observe that
Radius (r) = 6 in.
Height = 23 in.
Now,
We know that,
The volume of a hemisphere (V) = \(\frac{2}{3}\)πr³
So,
V = \(\frac{2}{3}\)π × 6³
= 144π in.³
Now,
We know that,
The volume of a cone (V’) = \(\frac{1}{3}\)πr²h
So,
V’ = \(\frac{1}{3}\)π × 6² × 23
= 276π in.³
So,
The volume of the remaining part of the solid = |144π – 276π|
= 132π
= 132 × 3.14
= 414.48 in.³
≈415 in.³
Hence, from the above,
We can conclude that the volume of the remaining part of the given solid is about 415 in.³

Question 15.
Higher-Order Thinking A student was asked to find the volume of a solid where the inner cylinder is hollow. She incorrectly said the volume is 2,034.72 cubic inches.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 69
Answer:
It is given that
A student was asked to find the volume of a solid where the inner cylinder is hollow. She incorrectly said the volume is 2,034.72 cubic inches.

a. Find the volume of the solid. Use 3.14 for π. Round to the nearest whole number.
Answer:
The given solid is:
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 69
Now,
From the given solid,
We can observe that it is a combination of a cone and a cylinder
So,
The volume of the given solid = The volume of a cylinder + The volume of a cone
Now,
From the given solid,
We can observe that
The radius of the cylinder is 3 in.
The height of the cylinder is 15 in.
The diameter of the cone is 12 in.
The slant height of the cone is 9 in.
Now,
We know that,
The volume of a cylinder (V) = πr²h
So,
V = 3.14 × 3² × 15
= 423.9 in.³
Now,
The volume of a cone:
We know that,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{12}{2}\)
r = 6 in.
Now,
We know that,
l² = r² + h²
So,
9² = 6² + h²
h² = 9² – 6²
h² = 45
h = 6.70 in.
Now,
We know that,
The volume of a cone (V’) = \(\frac{1}{3}\)πr²h
So,
V’ = \(\frac{1}{3}\) × 3.14 × 6² × 6.70
= 252.45 in.³
So,
The volume of the given solid = 423.9 + 252.45
= 676.3 in.³
≈676 in.³
Hence, from the above,
We can conclude that the volume of the given solid is about 676 in.³

b. What mistake might the student have made?
Answer:

Assessment Practice
Question 16.
The spherical boulder is 20 feet in diameter and weighs almost 8 tons. Find its volume. Use 3.14 for π. Round to the nearest cubic foot.
Answer:
It is given that
The spherical boulder is 20 feet in diameter and weighs almost 8 tons.
Now,
We know that,
The volume of a sphere (V) = \(\frac{4}{3}\)πr³
Now,
We know that,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{20}{2}\)
r = 10 feet
So,
V = \(\frac{4}{3}\) × 3.14 × 10³
= 4,186.6 feet³
≈ 4,187 feet³
Hence, from the above,
We can conclude that the volume of the given spherical boulder is: 4,187 feet³

Question 17.
A bowl is in the shape of a hemisphere (half a sphere) with a diameter of 13 inches. Find the volume of the bowl. Use 3.14 for π, and round to the nearest cubic inch.
Answer:
It is given that
A bowl is in the shape of a hemisphere (half a sphere) with a diameter of 13 inches. Find the volume of the bowl
Now,
We know that,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{13}{2}\)
r = 6.5 inches
Now,
We know that,
The volume of a hemisphere (V) = \(\frac{2}{3}\)πr³
So,
V = \(\frac{2}{3}\) × 3.14 × (6.5)³
= 574.88 inches³
≈ 575 inches³
Hence, from the above,
We can conclude that the volume of the given bowl is about 575 inches³

3-ACT MATH

3-Act Mathematical Modeling:
Measure Up
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 70

ACT 1
1. After watching the video, what is the first question that comes to mind?
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 71
Answer:

Question 2.
Write the Main Question you will answer.
Answer:

Question 3.
Construct Arguments Predict an answer to this Main Question. Explain your prediction.
Answer:

Question 4.
On the number line below, write a number that is too small to be the answer. Write a number that is too large.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 72
Answer:

Question 5.
Plot your prediction on the same number line.
Answer:

ACT 2
Question 6.
What information in this situation would be helpful to know? How would you use that information?
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 73
Answer:

Question 7.
Use Appropriate Tools What tools can you use to solve the problem? Explain how you would use them strategically.
Answer:

Question 8.
Model with Math
Represent the situation using mathematics. Use your representation to answer the Main Question.
Answer:

Question 9.
What is your answer to the Main Question? Is it higher or lower than your prediction? Explain why.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 74
Answer:

ACT 3
Question 10.
Write the answer you saw in the video.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 75
Answer:

Question 11.
Reasoning Does your answer match the answer in the video? If not, what are some reasons that would explain the difference?
Answer:

Question 12.
Make Sense and Persevere Would you change your model now that you know the answer? Explain.
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 76
Answer:

ACT 3 Extension
Reflect
Question 13.
Model with Math
Explain how you used a mathematical model to represent the situation. How did the model help you answer the Main Question?
Answer:

Question 14.
Make Sense and Persevere When did you struggle most while solving the problem? How did you overcome that obstacle?
Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 77
Answer:

SEQUEL
Question 15.
Generalize Suppose you have a graduated cylinder half the height of the one in the video. How wide does the cylinder need to be to hold the liquid in the flask?
Answer:

Topic 8 REVIEW

Topic Essential Question
How can you find volumes and surface areas of three-dimensional figures?
Answer:
The “Surface area” is the sum of the areas of all faces (or surfaces) on a 3D shape.
Ex:
A cuboid has 6 rectangular faces. To find the surface area of a cuboid, add the areas of all 6 faces
We know that,
The volume of a three-dimensional figure = Cross-sectional area × length

Vocabulary Review
Complete each definition and then provide an example of each vocabulary word.
Vocabulary
composite figure
cone
cylinder
sphere

Envision Math Common Core 8th Grade Answers Topic 8 Solve Problems Involving Surface Area And Volume 78
Answer:

Use Vocabulary in Writing
Draw a composite figure that includes any two of the following: a cylinder, a cone, a sphere, and a hemisphere. Label each part of your drawing. Then describe each part of your composite figure. Use vocabulary terms in your description.

Concepts and Skills Review

Lesson 8.1 Find Surface Area of Three-Dimensional Figures

Quick Review
Surface area is the total area of the surfaces of a three-dimensional figure. The chart gives formulas for finding the surface area of a cylinder, a cone, and a sphere.
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 79

Example
What is the surface area of the cylinder? Use 3.14 for π.
Answer:
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 80

Practice
Question 1.
What is the surface area of the cone? Use 3.14 for π.
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 81
Answer:
The given figure is:
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 81
From the given figure,
We can observe that
The slant height of the cone (l) is: 13 m
The radius of the cone (r) is: 5 m
Now,
We know that,
The surface area of a cone (S.A) = πr² + πrl
So,
S.A = 3.14 × 5² + 3.14 × 5 × 13
= 78.5 + 204.1
= 282.6 m²
Hence, from the above,
We can conclude that the surface area of the given cone is: 282.6 m²

Question 2.
What is the surface area of the sphere in terms of π?
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 82
Answer:
The given figure is:
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 82
From the given figure,
We can observe that
The diameter of the sphere (d) is: 10 cm
Now,
We know that,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{10}{2}\)
r = 5 cm
Now,
We know that,
The surface area of a sphere (S.A) = 4πr²
So,
S.A = 4 × 3.14 × 5²
= 314 cm²
Hence, from the above,
We can conclude that the surface area of the given sphere is: 314 cm²

Question 3.
What is the surface area of the cylinder in terms of π?
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 83
Answer:
The given figure is:
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 83
Now,
From the given figure,
We can observe that,
The diameter of the cylinder (d) is 12 in.
The height of the cylinder (h) is 15 in.
Now,
We know that,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{12}{2}\)
r = 6 in.
Now,
We know that,
The surface area of a cylinder (S.A) = 2πr² + 2πrh
So,
S.A = 2 × 3.14 × 6² + 2 × 3.14 × 6 × 15
= 226.08 + 565.2
= 791.28 in.³
Hence, from the above,
We can conclude that the surface area of the given cylinder is: 791.28 in.³

Lesson 8.2 Find Volume of Cylinders

Quick Review
The volume of a cylinder is equal to the area of its base times its height.
V = area of base · height, or V = πr²h
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 84

Example
What is the volume of the cylinder? Use 3.14 for π.
Answer:
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 85

Practice
Question 1.
What is the volume of the cylinder in terms of π?
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 86
Answer:
The given figure is:
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 86
From the given figure,
We can observe that
The diameter of the cylinder (d) is: 2 m
The height of the cylinder (h) is: 6 m
Now,
We know that,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{2}{2}\)
r = 1 m
Now,
We know that,
The volume of a cylinder (V) = πr²h
So,
V = 3.14 × 1² × 6
= 18.84 m³
Hence, from the above,
We can conclude that the volume of the given cylinder is: 18.84 m³

Question 2.
The volume of the cylinder is 141.3 cubic centimeters. What is the radius of the cylinder? Use 3.14 for π.
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 87
Answer:
It is given that
The volume of the cylinder is 141.3 cubic centimeters
Now,
The given figure is:
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 87
Now,
From the given figure,
We can observe that
The height of the cylinder (h) is: 5 cm
Now,
We know that,
The volume of a cylinder (V) = πr²h
So,
141.3 = 3.14 × r² × 5
r² = \(\frac{141.3}{3.14 × 5}\)
r²= 9
r = 3 cm
Hence, from the above,
We can conclude that the radius of the given cylinder is: 3 cm

Lesson 8.3 Find Volume of Cones

Quick Review
To find the volume of a cone, use the formula V = \(\frac{1}{3}\)πr2h.

Example
What is the volume of the cone? Use 3.14 for π.
Answer:
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 88

Practice
Question 1.
What is the volume of the cone in terms of π?
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 89
Answer:
The given figure is:
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 89
Now,
From the given figure,
We can observe that
The radius of the cone (r) is 3 in.
The height of the cone (h) is 8 in.
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × 3.14 × 3² × 8
= 75.36 in.³
Hence, from the above,
We can conclude that the volume of the given cone is: 75.36 in.³

Question 2.
What is the volume of the cone? Use 3.14 for π.
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 90
Answer:
The given figure is:
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 90
Now,
From the given figure,
We can observe that
The radius of the cone (r) is: 4 cm
The slant height of the cone (h) is: 5 cm
Now,
We know that,
l² = r² + h²
5² = 4² + h²
h² = 5² – 4²
h² = 9
h = 3 cm
Now,
We know that,
The volume of a cone (V) = \(\frac{1}{3}\)πr²h
So,
V = \(\frac{1}{3}\) × 3.14 × 4² × 3
= 50.24 cm³
Hence, from the above,
We can conclude that the volume of the given cone is: 50.24 cm³

Lesson 8.4 Find Volume of Spheres

Quick Review
To find the volume of a sphere, use the formula V = \(\frac{4}{3}\)πr3
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 91

Example
Find the volume of the composite figure. Use 3.14 for π.
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 92
Answer:
First, find the volume of the sphere. Use 3.14 for π.
V = \(\frac{4}{3}\)πr3
= \(\frac{4}{3}\)π(3.5)3 → Substitute 3.5 for r.
= 57.17π ≈ 179.5 cm3
Divide by 2 to find the volume of the hemisphere: 179.5 ÷ 2 ≈ 89.75 cubic centimeters.
Then, find the volume of the cone. Use 3.14 for π.
V = \(\frac{1}{3}\)πr2 h
= \(\frac{1}{3}\)π(3.5)2(14) → Substitute 3.5 for r and 14 for h.
= 57.171 ≈ 179.5 cm3
The volume of the composite figure is approximately 89.75 + 179.5 ≈ 269.25 cubic centimeters.

Practice
Question 1.
What is the volume of the sphere? Use \(\frac{22}{7}\) for π.
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 93
Answer:
The given figure is:
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 93
Now,
From the given figure,
We can observe that
The radius of the sphere (r) is: 14 cm
Now,
We know that,
The volume of a sphere (V) = \(\frac{4}{3}\)πr³
So,
V = \(\frac{4}{3}\) × \(\frac{22}{7}\) × 14³
= 11,498.6 cm³
Hence, from the above,
We can conclude that the volume of the given sphere is: 11,498.6 cm³

Question 2.
The surface area of a sphere is 1,017.36 square inches. What is the volume of the sphere? Use \(\frac{22}{7}\) for π.
Answer:
It is given that
The surface area of a sphere is 1,017.36 square inches.
Now,
We know that,
The surface area of a sphere (S.A) = 4πr²
So,
4πr² = 1,017.36
r² = \(\frac{1,017.36}{4π}\)
r² = 80.92
r = 8.99 inches
Now,
We know that,
The volume of a sphere (V) = \(\frac{4}{3}\)πr³
So,
V = \(\frac{4}{3}\) × \(\frac{22}{7}\) × (8.99)³
= 3,044.68 inches³
Hence, from the above,
We can conclude that the volume of the given sphere is: 3,044.68 inches³

Question 3.
What is the volume of the composite figure? Use \(\frac{22}{7}\) for π.
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 94
Answer:
The given figure is:
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 94
Now,
From the above,
We can observe that the given figure is a combination of a hemisphere and a cone
So,
The volume of the given figure = The volume of a hemisphere + The volume of a cone
Now,
From the given figure,
We can observe that
Diameter (d) = 4 cm
Height (h) = 10 cm
Now,
We know that,
Radius (r) = \(\frac{Diameter}{2}\)
r = \(\frac{4}{2}\)
r = 2 cm
Now,
We know that,
The volume of a hemisphere (V) = \(\frac{2}{3}\)πr³
So,
V = \(\frac{2}{3}\) × \(\frac{22}{7}\) × 2³
= 16.76 cm³
Now,
We know that,
The volume of a cone (V’) = \(\frac{1}{3}\)πr²h
So,
V’ = \(\frac{1}{3}\) × \(\frac{22}{7}\) × 2² × 10
= 41.90 cm³
So,
The volume of the given figure = 41.90 + 16.76
= 58.66 cm³
Hence, from the above,
We can conclude that the volume of the given figure is: 58.66 cm³

Topic 8 Fluency Practice

Hidden Clue
For each ordered pair, solve the equation to find the unknown coordinate. Then locate and label the corresponding point on the graph. Draw line segments to connect the points in alphabetical order. Use the completed picture to help answer the riddle below.
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 95

What do squares, triangles, pentagons, and octagons have in common?
Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 96

Envision Math Common Core Grade 8 Answer Key Topic 8 Solve Problems Involving Surface Area And Volume 97
Answer:
Step 1:
For each ordered pair, solve the equation to find the unknown coordinate.

Step 2:
Then locate and label the corresponding point on the graph.
Step 3:
Draw line segments to connect the points in alphabetical order.

Step 4:
Use the completed picture to help answer the riddle below.
All the squares, triangles, pentagons, and octagons have in common the sum of all the total angles i.e., 360°

enVision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem

Go through the enVision Math Common Core Grade 8 Answer Key Topic 7 Understand and Apply the Pythagorean Theorem and finish your homework or assignments.

enVision Math Common Core 8th Grade Answers Key Topic 7 Understand And Apply The Pythagorean Theorem

Topic Essential Question
How can you use the Pythagorean Theorem to solve problems?
Answer:
The Pythagorean Theorem is used to calculate the steepness of slopes of hills or mountains. A surveyor looks through a telescope toward a measuring stick a fixed distance away, so that the telescope’s line of sight and the measuring stick form a right angle.

3-ACT MATH OOO

Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 1
Go with the Flow
You may have noticed that when you double the base and the height of a triangle, the area is more than doubled. The same is true for doubling the sides of a square or the radius of a circle. So what is the relationship? Think about this during the 3-Act Mathematical Modeling lesson.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 2

Topic 7 enVision STEM Project

Did You Know?
Over two billion people will face water shortages by 2050 according to a 2015 United Nations Environment Program report.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 3
Rainwater can be collected and stored for use in irrigation, industrial uses, flushing toilets, washing clothes and cars, or it can be purified for use as everyday drinking water.
This alternative water source reduces the use of fresh water from reservoirs and wells.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 4
Using water wisely saves money on water and energy bills and extends the life of supply and wastewater facilities.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 5
Roofs of buildings or large tarps are used to collect rainwater.
A rainwater collection system for a building roof that measures 28 feet by 40 feet can provide 700 gallons of water-enough water to support two people for a year—from a rainfall of 1.0 inch.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 6
Even a 5 foot by 7-foot tarp can collect 2 gallons of water from a rainfall total of only 0.1 in.

The rainwater harvesting market is expected to grow 5% from 2016 to 2020.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 7

Your Task: Rainy Days
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 8
Rainwater collection is an inexpensive way to save water in areas where it is scarce. One inch of rain falling on a square roof with an area of 100 ft² collects 62 gallons of water that weighs over 500 pounds. You and your classmates will research the necessary components of a rainwater collection system. Then you will use what you know about right triangles to design a slanted roof system that will be used to collect rainwater.
Answer:
It is given that
Rainwater collection is an inexpensive way to save water in areas where it is scarce. One inch of rain falling on a square roof with an area of 100 ft² collects 62 gallons of water that weighs over 500 pounds
Now,
The necessary components of a rainwater collection system are:
A) Catchments B) Coarse mesh C) Gutters D) Conduits E) First-flushing F) Filter G) Storage facility H) Recharge Structures

Topic 7 GET READY!

Review What You Know!

Vocabulary
Choose the best term from the box to complete each definition.
cube root
diagonal
isosceles triangle
perimeter
right triangle
square root

Question 1.
The __________ of a number is a factor that when multiplied by itself gives the number.
Answer:
We know that,
The “Square root” of a number is a factor that when multiplied by itself gives the number
Hence, from the above,
We can conclude that the best term to complete the given definition is a “Square root”

Question 2.
A _________ is a line segment that connects two vertices of a polygon and is not the side.
Answer:
We know that,
A “Diagonal” is a line segment that connects two vertices of a polygon and is not the side
Hence, from the above,
We can conclude that the best term to complete the given definition is a “Diagonal”

Question 3.
The _________ of a figure is the distance around it.
Answer:
We know that,
The “Perimeter” of a figure is the distance around it
Hence, from the above,
We can conclude that the best term to complete the given definition is the “Perimeter”

Question 4.
A ___________ is a triangle with one right angle.
Answer:
We know that,
A “Right triangle” is a triangle with one right angle
Hence, from the above,
We can conclude that the best term to complete the given definition is a “Right angle”

Simplify Expressions with Exponents

Simplify the expression.
Question 5.
32 + 42
Answer:
The given expression is: 32 + 42
So,
32 + 42
= (3 × 3) + (4 × 4)
= 9 + 16
= 25

Question 6.
22 + 52
Answer:
The given expression is: 22 + 52
So,
2² + 52
= (2 × 2) + (5 × 5)
= 4 + 25
= 29

Question 7.
102 – 82
Answer:
The given expression is: 102 – 82
So,
102 – 82
= (10 × 10) – (8 × 8)
= 100 – 64
= 36

Square Roots

Determine the square root.
Question 8.
\(\sqrt {81}\)
Answer:
The given expression is: \(\sqrt{81}\)
Hence,
\(\sqrt{81}\) = 9

Question 9.
\(\sqrt {144}\)
Answer:
The given expression is: \(\sqrt{144}\)
Hence,
\(\sqrt{144}\) = 12

Question 10.
\(\sqrt {225}\)
Answer:
The given expression is: \(\sqrt{225}\)
Hence,
\(\sqrt{225}\) = 15

Distance on a Coordinate Plane

Determine the distance between the two points.
Question 11.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 9
Answer:
The given graph is:
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 9
From the given graph,
The given points are: (2, 5), (7, 5)
Now,
Compare the given points with (x1, y1), (x2, y2)
We know that,
Distance between 2 points = √(x2 – x1)2 + (y2 – y1)2
= √(7 – 2)2 + (5 – 5)2
= \(\sqrt{5²}\)
= 5 units
Hence, from the above,
We can conclude that the distance between the given points is: 5 units

Question 12.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 10
Answer:
The given graph is:
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 10
From the given graph,
The given points are: (3, 2), (3, 9)
Now,
Compare the given points with (x1, y1), (x2, y2)
We know that,
Distance between 2 points =√(x2 – x1)2 + (y2 – y1)2
= √(3 – 3)2 + (9 – 2)2
= \(\sqrt{7²}\)
= 7 units
Hence, from the above,
We can conclude that the distance between the given points is: 7 units

Language Development

Complete the word map using key terms, examples, or illustrations related to the Pythagorean Theorem and its Converse.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 11
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 12
Answer:

Topic 7 PICK A PROJECT

PROJECT 7A
Where would you like to bike ride in your neighborhood?
PROJECT: PLAN A METRIC CENTURY RIDE
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 13

PROJECT 7B
What designs have you seen on kites?
PROJECT: BUILD A KITE
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 14

PROJECT 7C
What buildings in your community have unusual shapes as part of their structure or design?
PROJECT: MAKE A SCRAPBOOK
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 15

PROJECT 7D
What geometric designs have you noticed on your clothes?
PROJECT: DESIGN A FABRIC TEMPLATE
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 16

3-ACT MATH

3-Act Mathematical Modeling: Go with the Flow

Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 17

АСТ 1
Question 1.
After watching the video, what is the first question that comes to mind?
Answer:

Question 2.
Write the Main Question you will answer.
Answer:

Question 3.
Make a prediction to answer this Main Question.
_________ % will fit in the third square.
Answer:

Question 4.
Construct Arguments Explain how you arrived at your prediction.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 18
Answer:

ACT 2
Question 5.
What information in this situation would be helpful to know? How would you use that information?
Answer:

Question 6.
Use Appropriate Tools What tools can you use to solve the problem? Explain how you would use them strategically.
Answer:

Question 7.
Model With Math
Represent the situation using mathematics. Use your representation to answer the Main Question.
Answer:

Question 8.
What is your answer to the Main Question? Does it differ from your prediction? Explain.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 19
Answer:

АСТ 3
Question 9.
Write the answer you saw in the video.
Answer:

Question 10.
Reasoning Does your answer match the answer in the video? If not, what are some reasons that would explain the difference?
Answer:

Question 11.
Make Sense and Persevere Would you change your model now that you know the answer? Explain.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 20
Answer:

Act 3
Extension
Reflect
Question 12.
Model with Math
Explain how you used a mathematical model to represent the situation. How did the model help you answer the Main Question?
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 21
Answer:

Question 13.
Reason Abstractly How did you represent the situation using symbols? How did you use those symbols to solve the problem?
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 22
Answer:

SEQUEL
Question 14.
Construct Arguments Explain why you can use an area formula when the problem involves comparing volumes.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 23
Answer:

Lesson 7.1 Understand the Pythagorean Theorem

Explain It!
Kelly drew a right triangle on graph paper. Kelly says that the sum of the areas of squares with side lengths a and b is the same as the area of a square with side length c.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 24

I can… use the Pythagorean Theorem to find unknown sides of triangles.

A. Do you agree with Kelly? Explain.
Answer:
It is given that
Kelly drew a right triangle on graph paper. Kelly says that the sum of the areas of squares with side lengths a and b is the same as the area of a square with side length c.
We know that,
According to the Pythagorean theorem,
Hypotenuse² = Side length 1² + Side length 2²
So,
From the given graph,
We can observe that
Side length 1 is: a
Side length 2 is: b
The hypotenuse is: c
So,
c² = a² + b²
Hence, from the above,
We can conclude that we can agree with Kelly

B. Sam drew a different right triangle with side lengths a = 5, b = 12, and c = 13. Is the relationship Kelly described true for Sam’s right triangle? Explain.
Answer:
It is given that
Sam drew a different right triangle with side lengths a = 5, b = 12, and c = 13
Now,
From part (a),
The relation according to Kelly is:
c² = a² + b²
So,
13² = 12² + 5²
169 = 144 + 25
169 = 169
Hence, from the above,
We can conclude that the relationship Kelly described is true for Sam’s right-angled triangle

Focus on math practices
Generalize Kelly draws another right triangle. What would you expect to be the relationship between the areas of the squares drawn on each side of the triangle? Explain.
Answer:
It is given that Kelly draws another right triangle
Hence,
If in a triangle, the square on one of the sides equals the sum of the squares on the remaining two sides of the triangle, then the angle contained by the remaining two sides of the triangle is right.”

Essential Question
How does the Pythagorean Theorem relate to the side lengths of a right triangle?
Answer:
The Pythagorean equation relates the sides of a right triangle in a simple way so that if the lengths of any two sides are known the length of the third side can be found. Another corollary of the theorem is that in any right triangle, the hypotenuse is greater than any one of the other sides but less than their sum.

Try It!

A right triangle has side lengths 15 centimeters, 25 centimeters, and 20 centimeters. How can you use the Pythagorean Theorem to write an equation that describes how the side lengths are related?
a2 + b2 = c2
_______2 + ________2 = _________2
_________ + _________ = ________
Answer:
It is given that
A right triangle has side lengths 15 centimeters, 25 centimeters, and 20 centimeters.
We know that,
According to the Pythagorean Theorem,
The hypotenuse has the greatest length in the right triangle
Now,
Let the hypotenuse be c
Let the other two sides be a and b
So,
From the given information,
c = 25 centimeters, a = 15 centimeters,and b = 20 centimeters
So,
According to the Pythagorean Theorem,
25² = 15² + 20²
625 = 225 + 400
625 = 625
Hence, from the above,
We can conclude that we proved how the Pythagorean Theorem relates to the lengths of the right triangle

Convince Me!
How do you know that the geometric proof of the Pythagorean Theorem shown above can be applied to all right triangles?
Answer:
It can be proven using the law of cosines or as follows: Let ABC be a triangle with side lengths a, b, and c, with a2 + b2 = c2.  Therefore, the angle between the side of lengths a and b in the original triangle is a right angle. This proof of the converse makes use of the Pythagorean theorem itself.

Try It!

A right triangle has a hypotenuse length of 32 meters. It has one leg with a length of 18 meters. What is the length of the other leg? Express your answer as a square root.
Answer:
It is given that
A right triangle has a hypotenuse length of 32 meters. It has one leg with a length of 18 meters.
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the hypotenuse
a and b are the legs
Now,
Let the other leg be x
So,
32² = 18² + x²
x² = 32² – 18²
x² = 1024 – 324
x² = 700
x = \(\sqrt{700}\)
Hence, from the above,
We can conclude that the length of the other leg is: \(\sqrt{700}\)

KEY CONCEPT

The Pythagorean Theorem is an equation that relates the side lengths of a right triangle, a2 + b2 = c2, where a and b are the legs of a right triangle and c is the hypotenuse.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 25

Do You Understand?
Question 1.
Essential Question How does the Pythagorean Theorem relate to the side lengths of a right triangle?
Answer:
The Pythagorean equation relates the sides of a right triangle in a simple way so that if the lengths of any two sides are known the length of the third side can be found. Another corollary of the theorem is that in any right triangle, the hypotenuse is greater than any one of the other sides but less than their sum.

Question 2.
Use Structure A side of each of the three squares forms a side of a right triangle.
Would any three squares form the sides of a right triangle? Explain.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 26
Answer:
It is given that
A side of each of the three squares forms a side of a right triangle.
Now,
We know that,
The length of all the sides in a square is equal
Now,
From the given figure,
We can observe that
Each side of a square from the three squares form a right triangle
Hence, from the above,
We can conclude that the three squares form the sides of a right triangle

Question 3.
Construct Arguments Xavier said the missing length is about 18.5 units. Without calculating, how can you tell that Xavier solved incorrectly?
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 27
Answer:
It is given that
Xavier said the missing length is about 18.5 units
Now,
We know that,
According to the Pythagorean Theorem,
The length of the hypotenuse is the greatest
Now,
The given right triangle is:
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 27
So,
According to the Pythagorean Theorem,
The length of the missing side should be greater than 21 and 26
Hence, from the above,
We can conclude that Xavier calculated incorrectly

Do You Know How?
Question 4.
A right triangle has leg lengths of 4 inches and 5 inches. What is the length of the hypotenuse? Write the answer as a square root and round to the nearest tenth of an inch.
Answer:
It is given that
A right triangle has leg lengths of 4 inches and 5 inches
Now,
We know that,
According to the Pythagorean theorem,
c² = a²+ b²
Where,
c is the length of the hypotenuse
a and b are the lengths of the legs
So,
c² = 4² + 5²
c² = 16 + 25
c² = 41
c = \(\sqrt{41}\)
c = 6.4 inches
Hence, from the above,
We can conclude that the length of the hypotenuse is: 6.4 inches

Question 5.
Find the missing side length to the nearest tenth of afoot.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 28
Answer:
The given right triangle is:
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 28
Now,
We know that,
According to the Pythagorean theorem,
c² = a²+ b²
Where,
c is the length of the hypotenuse
a and b are the lengths of the legs
So,
14² = 8² + b²
b²= 14² – 8²
b² = 196 – 64
b² = 132
b = \(\sqrt{132}\)
b = 11.5 feet
Hence, from the above,
We can conclude that the length of the missing side is: 11.5 feet

Question 6.
Find the missing side length to the nearest tenth of a millimeter.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 29
Answer:
The given right triangle is:
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 29
Now,
We know that,
According to the Pythagorean theorem,
c² = a²+ b²
Where,
c is the length of the hypotenuse
a and b are the lengths of the legs
So,
c² = (3.7)² + (7.5)²
c² = 13.69 + 56.25
c² = 69.94
c = \(\sqrt{69.94}\)
c = 8.4 mm
Hence, from the above,
We can conclude that the length of the missing side is: 8.4 mm

Practice & Problem Solving

Leveled Practice In 7 and 8, find the missing side length of each triangle.
Question 7.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 30
The length of the hypotenuse is ________ units.
Answer:

Question 8.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 31
The length of leg b is about ________ inches.
Answer:

Question 9.
What is the length of the hypotenuse of the triangle when x = 15? Round your answer to the nearest tenth of a unit.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 32
Answer:
The given right angle is:
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 32
Now,
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the length of the hypotenuse
a and b are the lengths of the legs
So,
c² = (3x)² + (4x + 4)²
Now,
When x = 15,
c² = (3 × 15)² + (4 × 15 + 4)²
c² = 45² + 64²
c² = 2,025 + 4,096
c² = 6,121
c = \(\sqrt{6,121}\)
c = 78.2 units
Hence, from the above,
We can conclude that the length of the hypotenuse when x= 15 is: 78.2 units

Question 10.
What is the length of the missing side rounded to the nearest tenth of a centimeter?
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 33
Answer:
The given right triangle is:
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 33
Now,
We know that,
According to the Pythagorean Theorem,
c² = a²+ b²
Where,
c is the length of the hypotenuse
a and b are the lengths of the legs
So,
a² = (12.9)² + (15.3)²
a² = 166.41 + 234.09
a² = 400.5
a = \(\sqrt{400.5}\)
a = 20 cm
Hence, from the above,
We can conclude that the length of the side a is: 20 cm

Question 11.
Use the Pythagorean Theorem to find the unknown side length of the right triangle.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 34
Answer:
The given right triangle is:
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 34
Now,
We know that,
According to the Pythagorean Theorem,
c² = a²+ b²
Where,
c is the length of the hypotenuse
a and b are the lengths of the legs
So,
c² = (10)² + (24)²
c² = 100 + 576
c² = 676
c = \(\sqrt{676}\)
c = 26 m
Hence, from the above,
We can conclude that the length of the side a is: 26 m

Question 12.
What is the length of the unknown leg of the right triangle rounded to the nearest tenth of afoot?
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 35
Answer:
The given right triangle is:
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 35
Now,
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the length of the hypotenuse
a and b are the lengths of the legs
So,
9² = 2² + b²
b² = 9² – 2²
b² = 81 – 4
b² = 77
b = \(\sqrt{77}\)
b = 8.8 foot
Hence, from the above,
We can conclude that the length of the unknown leg is: 8.8 foot

Question 13.
A student is asked to find the length of the hypotenuse of a right triangle. The length of one leg is 32 centimeters, and the length of the other leg is 26 centimeters. The student incorrectly says that the length of the hypotenuse is 7.6 centimeters.
a. Find the length of the hypotenuse of the right triangle to the nearest tenth of a centimeter.
Answer:
It is given that
A student is asked to find the length of the hypotenuse of a right triangle. The length of one leg is 32 centimeters, and the length of the other leg is 26 centimeters. The student incorrectly says that the length of the hypotenuse is 7.6 centimeters.
Now,
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the length of the hypotenuse
a and b are the lengths of the legs
So,
c² = 32² + 26²
c² = 1,024 + 676
c² = 1,700
c = \(\sqrt{1,700}\)
c = 41.2 centimeters
Hence, from the above,
We can conclude that the length of the hypotenuse of a right triangle is: 41.2 centimeters

b. What mistake might the student have made?
Answer:
It is given that
The student incorrectly says that the length of the hypotenuse is 7.6 centimeters.
But,
From part (a),
The length of the hypotenuse is: 41.2 centimeters
Hence, from the above,
We can conclude that the mistake the student might make is the misinterpretation of the length of the hypotenuse

Question 14.
Find the length of the unknown leg of the right triangle.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 36
Answer:
The given right triangle is:
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 36
Now,
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the length of the hypotenuse
a and b are the lengths of the legs
So,
(37.25)² = (12.25)² + b²
b² = (37.25)² – (12.25)²
b² = 1,387.56 – 150.06
b² = 1,237.5
b = \(\sqrt{1,237.5}\)
b = 35.17 units
Hence, from the above,
We can conclude that the length of the unknown leg is: 35.17 units

Question 15.
Higher-Order Thinking A right triangle has side lengths 12 centimeters and 14 centimeters. Name two possible side lengths for the third side, and explain how you solved for each.
Answer:
It is given that
A right triangle has side lengths of
12 centimeters and 14 centimeters.
Now,
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the length of the hypotenuse
a and b are the lengths of the legs
Now,
Let the length of the third side be x
So,
The possible lengths of the third side may be:
x < 12 centimeters and x > 14 centimeters
Hence, from the above,
We can conclude that the two possible side lengths for the third side are:
x < 12 centimeters and x > 14 centimeters

Assessment Practice
Question 16.
Which right triangle has a hypotenuse that is about 39 feet long?
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 37
Answer:
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the length of the hypotenuse
a and b are the lengths of the legs
So,
For Options A and D:
A) c² = 30² + 15²                     D) c² = 30² + 14²
= 33.54 ft                                 = 33.10 ft
For Options B and C:
B) c² = 36² + 12²                      C) c² = 36² + 15²
= 37.94 ft                                    = 39 ft
Hence, from the above,
We can conclude that Option C matches the given situation

Question 17.
Which right triangle does NOT have an unknown leg length of about 33 cm?
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 38
Answer:
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the length of the hypotenuse
a and b are the lengths of the legs
So,
For Options A and D:
A) b² = 35² – 11²                     D) b² = 34² – 9²
= 33.22 cm                              = 32.78 cm
For Options B and C:
B) b² = 30² – 10²                      C) b² = 35² – 12²
= 28.28 cm                              = 32.87 cm
Hence, from the above,
We can conclude that Option B matches the given situation

Lesson 7.2 Understand the Converse of the Pythagorean Theorem

Solve & Discuss It!
Kayla has some straws that she will use for an art project. She wants to glue three of the straws onto a sheet of paper, without overlapping, to make the outline of a right triangle. Which three straws could Kayla use to make a right triangle? Explain.
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 39
I can… use the Converse of the Pythagorean Theorem to identify right triangles.
Answer:
It is given that
Kayla has some straws that she will use for an art project. She wants to glue three of the straws onto a sheet of paper, without overlapping, to make the outline of a right triangle.
Now,
We know that,
The converse of the Pythagorean Theorem states that if the square of the third side of a triangle is equivalent to the sum of its two shorter sides, then it must be a right triangle i.e.,
If c² = a²+ b², then the given triangle is a right triangle
So,
From the given straws,
we can observe that
The straws numbered 3, 4, and 5 can be glued to make the outline of a right triangle
The straws numbered 5, 12, and 13 can be glued to make the outline of a right triangle
Hence, from the above,
We can conclude that there are 2 pairs of straws i.e., (3, 4, 5) and (12, 5, 13) to make the outline of a right triangle

Look for Relationships
How could you use the Pythagorean Theorem to determine whether the lengths form a right triangle?
Answer:
According to the converse of the Pythagorean Theorem,
If the square of the length of the longest side of a triangle is equal to the sum of the squares of the other two sides, then the triangle is a right triangle.

Focus on math practices
Use Structure Could Kayla use the straws that form a right triangle to make a triangle that is not a right triangle? Explain.
Answer:
From the given straws,
We can observe that the pair (6, 7, 4) can’t form a right triangle but (3, 4, 5) can form a right triangle
Hence, from the above,
We can conclude that Kayla can use the straws that form a right triangle to make a triangle that is not a right triangle

Essential Question
How can you determine whether a triangle is a right triangle?
Answer:
We can determine the triangle is a right triangle by using the converse of the Pythagorean Theorem
Hence,
According to the converse of the Pythagorean Theorem,
If the square of the length of the longest side of a triangle is equal to the sum of the squares of the other two sides, then the triangle is a right triangle.

Try It!

A triangle has side lengths 4 inches, 5 inches, and 7 inches. Is the triangle a right triangle?
Envision Math Common Core 8th Grade Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 40
Is a2 + b2 equal to c2? _______
Is the triangle a right triangle? _________
Answer:
It is given that
A triangle has side lengths 4 inches, 5 inches, and 7 inches.
Now,
We know that,
According to the converse of the Pythagorean Theorem,
If the square of the length of the longest side of a triangle is equal to the sum of the squares of the other two sides, then the triangle is a right triangle.
So,
c² = a² + b²
Where,
c is the hypotenuse that has the longest side length
a and b are the lengths of the legs
So,
7² = 4² + 5²
49 = 16 + 25
49 = 41
So,
49 ≠ 41
Hence, from the above,
We can conclude that
c² ≠ a²+ b²
The given triangle is not a right triangle

Convince Me!
Explain the proof of the Converse of the Pythagorean Theorem in your own words.
Answer:
The converse of the Pythagorean Theorem is:
If the square of the length of the longest side of a triangle is equal to the sum of the squares of the other two sides, then the triangle is a right triangle.

Try It!

A triangle has side lengths 10 feet, \(\sqrt {205}\) feet, and \(\sqrt {105}\) feet. Is this a right triangle? Explain.
Answer:
It is given that
A triangle has side lengths 10 feet, \(\sqrt {205}\) feet, and \(\sqrt {105}\) feet.
Now,
We know that,
According to the converse of the Pythagorean Theorem,
If
c² = a² + b², then
The given triangle is a right triangle
We know that,
c is the length of the hypotenuse that has the longest side in a right triangle
So,
(\(\sqrt{205}\))² =(\(\sqrt{105}\))² + 10²
205 = 105 + 100
205 = 205
So,
c² = a² + b²
Hence, from the above,
We can conclude that the triangle with the given side lengths is a right triangle

Try It!

A triangle is inside a trapezoid. Is the triangle a right triangle? Explain.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 41
Answer:
It is given that a triangle is inside a trapezoid
Now,
The given trapezoid is:
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 41
From the given trapezoid,
The sides of the triangle are: 17 in., 15 in., \(\sqrt{514}\) in.
Now,
We know that,
According to the converse of the Pythagorean Theorem,
If
c² = a² + b²,
then, the given triangle is a right triangle
So,
(\(\sqrt{514}\))² = 17² + 15²
514 = 289 + 225
514 = 514
So,
c² = a² + b²
Hence, from the above,
We can conclude that the triangle that is in the trapezoid is a right triangle

KEY CONCEPT

The Converse of the Pythagorean Theorem states that if the sum of the squares of the lengths of two sides of a triangle is equal to the square of the length of the third side, the triangle is a right triangle.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 42

Do You Understand?
Question 1.
Essential Question How can you determine whether a triangle is a right triangle?
Answer:
We can determine the triangle is a right triangle by using the converse of the Pythagorean Theorem
Hence,
According to the converse of the Pythagorean Theorem,
If the square of the length of the longest side of a triangle is equal to the sum of the squares of the other two sides, then the triangle is a right triangle.

Question 2.
Construct Arguments A triangle has side lengths of 3 centimeters, 5 centimeters, and 4 centimeters. Abe used the Converse of the Pythagorean Theorem to determine whether it is a right triangle.
32 + 52 \(\underline{\underline{?}}\) 42
9 + 25 \(\underline{\underline{?}}\) 16
34 ≠ 16
Abe concluded that it is not a right triangle. Is Abe correct? Explain.
Answer:
It is given that
A triangle has side lengths of 3 centimeters, 5 centimeters, and 4 centimeters
Now,
We know that,
According to the converse of the Pythagorean Theorem,
If
c² = a² + b²,
then, the triangle is  a right triangle
We know that,
The hypotenuse has the length of the longest side
So,
5²= 3² + 4²
25 = 9 + 16
25 = 25
So,
c² = a² + b²
Hence, from the above,
We can conclude that the given triangle is a right triangle and Abe is not correct

Question 3.
Use Structure When you are given three side lengths for a triangle, how do you know which length to substitute for a, b, or c in the Pythagorean Theorem?
Answer:
First, we will find the squares of all lengths, then we will check which two squares of sides are equal to the square of the third side as per Pythagoras theorem. Hence the two sides would according be a and b and the third side will become c

Do You Know How?
Question 4.
Is the triangle a right triangle? Explain.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 43
Answer:
The given triangle is:
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 43
We know that,
According to the converse of the Pythagorean Theorem,
If c² = a² + b²,
then, the triangle is a right triangle
So,
10² = 6² + 8²
100 = 36 + 64
100 = 100
So,
c² = a² + b²
Hence, from the above,
We can conclude that the given triangle is a right triangle

Question 5.
Is the triangle a right triangle? Explain.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 44
Answer:
The given triangle is:
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 44
We know that,
According to the converse of the Pythagorean Theorem,
If c² = a² + b²,
then, the triangle is a right triangle
So,
8² = (\(\sqrt{26}\))² + (\(\sqrt{28}\))²
64 = 26 + 28
64 = 54
So,
c² ≠ a² + b²
Hence, from the above,
We can conclude that the given triangle is not a right triangle

Question 6.
Is the purple triangle a right triangle? Explain.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 45
Answer:
The given triangle is:
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 45
We know that,
According to the converse of the Pythagorean Theorem,
If c² = a² + b²,
then, the triangle is a right triangle
So,
(20.8)² = 14² + (15.5)²
432.64 = 196 + 240.25
432.64 = 436.25
So,
c² ≠ a² + b²
Hence, from the above,
We can conclude that the purple triangle is not a right triangle

Practice & Problem Solving

Leveled Practice In 7 and 8, determine whether each triangle is a right triangle.
Question 7.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 46
Is the triangle a right triangle? ________
Answer:

Hence, from the above,
We can conclude that the given triangle is not a right triangle

Question 8.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 47
Is the triangle a right triangle? _________
Answer:

Hence, from the above,
We can conclude that the given triangle is a right triangle

Question 9.
Can the sides of a right triangle have lengths 5, 15, and \(\sqrt {250}\)? Explain.
Answer:
We know that,
According to the converse of the Pythagorean Theorem,
If
c² = a² + b²,
then, the triangle is a right triangle
The hypotenuse has the longest side length
So,
(\(\sqrt{250}\))² = 5² + 15²
250 = 25 + 225
250 = 250
Hence, from the above,
We can conclude that the sides of a right triangle have lengths 5, 15, and \(\sqrt {250}\)

Question 10.
Is ∆PQR a right triangle? Explain.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 48
Answer:
The given triangle is:
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 48
We know that,
According to the converse of the Pythagorean Theorem,
If c² = a² + b²,
then, the triangle is a right triangle
So,
(6.25)² = (3.75)² + 5²
39.0625 = 14.0625 + 25
39.0625 = 39.0625
So,
c² = a² + b²
Hence, from the above,
We can conclude that ΔPQR is a right triangle

Question 11.
The green triangle is set inside a rectangle. Is the green triangle a right triangle? Explain.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 49
Answer:
It is given that
The green triangle is set inside a rectangle
Now,
The given figure is:
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 49
We know that,
According to the converse of the Pythagorean Theorem,
If c² = a² + b²,
then, the triangle is a right triangle
So,
21² = (\(\sqrt{282}\))² + (\(\sqrt{159}\))²
441 = 282 + 159
441 = 441
So,
c² = a² + b²
Hence, from the above,
We can conclude that the given green triangle is a right triangle

Question 12.
The side lengths of three triangles are shown. Which of the triangles are right triangles?
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 50
Answer:
It is given that
The side lengths of the three triangles are shown in the table
Now,
The given table is:
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 50
Now,
We know that,
According to the converse of the Pythagorean Theorem,
If c² = a² + b²,
then, the triangle is a right triangle
So
For Triangle 1,
(\(\frac{5}{7}\))² = (\(\frac{3}{7}\))² + (\(\frac{4}{7}\))²
25 = 16 + 9
25 = 25
For Triangle 2,
15² = 8² + 8²
225 = 64 + 64
225 = 128
For Triangle 3,
(\(\frac{13}{17}\))² = (\(\frac{12}{17}\))² + (\(\frac{5}{17}\))²
169 = 144 + 25
169 = 169
So,
The condition
c² = a² + b²
is true for the Triangles 1 and 3
Hence, from the above,
We can conclude that Triangle 1 and Triangle 3 is a right triangle

Question 13.
Construct Arguments Three students draw triangles with the side lengths shown. All three say that their triangle is a right triangle. Which students are incorrect? What mistake might they have made?
Student 1: 22, 33, 55
Student 2: 44, 33, 77
Student 3: 33, 44, 55
Answer:
It is given that
Three students draw triangles with the side lengths shown. All three say that their triangle is a right triangle.
Now,
We know that,
According to the converse of the Pythagorean Theorem,
If
c² = a² + b²,
then, the triangle is a right triangle
Now,
For student 1,
55² = 33² + 22²
3,025 = 1,089 + 484
3,025 = 1,573
For student 2,
77²= 44² + 33²
5,929 = 1,936 + 1,089
5,929 = 3,025
For student 3,
55² = 44² + 33²
3,025 = 1,936 + 1,089
3,025 = 3,025
So,
The condition
c² = a² + b²
is false for the side lengths of the triangles that are drawn by students 1 and 2
Hence, from the above,
We can conclude that student 1 and student 2 are incorrect

Question 14.
Model with Math
∆JKL is an isosceles triangle. Is KM the height of ∆JKL? Explain.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 51
Answer:
It is given that
ΔJKL is an isosceles triangle
Now,
To find whether KM is the height of ΔJKL,
Find out whether ΔKLM is a right triangle or not
Now,
The given triangle is:
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 51
Now,
We know that,
According to the converse of the Pythagorean Theorem,
c² = a²+ b²
So,
From ΔKLM,
(\(\sqrt{340}\))² = 13² + 14²
340 = 169 + 196
340 = 365
So,
c² ≠ a² + b²
So,
ΔKLM is not a right triangle
Hence, from the above,
We can conclude that KM is not the height of ΔJKL

Question 15.
Higher-Order Thinking The side lengths of three triangles are given.
Triangle 1: \(\sqrt{229}\) units, \(\sqrt{225}\) units, 22 units
Triangle 2: \(\sqrt{11 \frac{1}{3}}\) units, \(\sqrt{13 \frac{2}{3}}\) units, 5 units
Triangle 3: 16 units, 17 units, \(\sqrt{545}\) units
a. Which lengths represent the side lengths of a right triangle?
Answer:
We know that,
According to the converse of the Pythagorean Theorem,
If
c² = a² + b²
then, the triangle is a right triangle
Now,
For Triangle 1,
(\(\sqrt{229}\))² = (\(\sqrt{225}\))² + 22²
229 = 225 + 484
229 = 709
For Triangle 2,
(\(\sqrt{\frac{41}{3}}\))² + (\(\sqrt{\frac{34}{3}}\))² = 5²
\(\frac{41}{3}\) + \(\frac{34}{3}\) = 25
25 = 25
For Triangle 3,
(\(\sqrt{545}\))² = 16² + 17²
545 = 256 + 289
545 = 545
So,
The condition
c² = a²+ b²
is true for triangle 2 and triangle 3
Hence, from the above,
We can conclude that Triangle 2 and Triangle 3 represent the side lengths of a triangle

b. For any triangles that are not right triangles, use two of the sides to make a right triangle.
Answer:

Assessment Practice
Question 16.
Which shaded triangle is a right triangle? Explain.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 52
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 52
Now,
We know that,
According to the converse of the Pythagorean Theorem,
If
c² = a²+ b²,
then the triangle is a right triangle
Now,
For ΔABC,
144² = 63² + (\(\sqrt{9}\))²
20,736 = 3,969 + 9
20,736 = 3,978
For ΔXYZ,
(\(\sqrt{144}\))² = (\(\sqrt{63}\))² + 9²
144 = 63 + 81
144 = 144
So,
The condition c² = a²+ b² is true for the shaded triangle XYZ
Hence, from the above,
We can conclude that the shaded triangle ΔXYZ is a right triangle

Question 17.
Which triangle is a right triangle?
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 53
A. Triangle I only
B. Triangle II only
C. Triangle I and Triangle II
D. Neither Triangle I nor Triangle II
Answer:
The given triangles are:
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 53
Now,
We know that,
According to the converse of the Pythagorean Theorem,
If
c² = a² + b²,
then the triangle is a right triangle
Now,
For Triangle I,
52² = 40² + 48²
2,704 = 1,600 + 2,304
2,704 = 3,904
For Triangle II,
65² = 60² + 25²
4,225 = 3,600 + 625
4,225 = 4,225
Hence, from the above,
We can conclude that Triangle II only is a right triangle

Topic 7 MID-TOPIC CHECKPOINT

Question 1.
Vocabulary How are the hypotenuse and the legs of a right triangle related? Lesson 7-1
Answer:
The relation between the sides and angles of a right triangle is the basis for trigonometry. The side opposite the right angle is called the hypotenuse. The sides adjacent to the right angle are called legs

Question 2.
Given that ∆QPR has side lengths of 12.5 centimeters, 30 centimeters, and 32.5 centimeters, proves ∆QPR is a right triangle. Lesson 7-2
Answer:
It is given that
∆QPR has side lengths of 12.5 centimeters, 30 centimeters, and 32.5 centimeters
Now,
We know that,
According to the converse of the Pythagorean Theorem,
If
c² = a² + b²,
then, the triangle is a right triangle
So,
(32.5)² = (12.5)² + 30²
1,056.25 = 156.25 + 900
1,056.25 = 1,056.25
So,
The condition
c² = a² + b²
is true for the given side lengths of a triangle
Hence, from the above,
We can conclude that ΔQPR is a right triangle

Question 3.
Ella said that if she knows the lengths of just two sides of any triangle, then she can find the length of the third side by using the Pythagorean Theorem. Is Ella correct? Explain. Lesson 7-1
Answer:
Ella said that if she knows the lengths of just two sides of any triangle, then she can find the length of the third side by using the Pythagorean Theorem.
Now,
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the hypotenuse
a and b are the legs
Now,
If we know a and b, then we can find c
If we know b and c, then we can find a
If we know a and c, then we can find b
Hence, from the above,
We can conclude that Ella is correct

Question 4.
Find the unknown side length. Round to the nearest tenth. Lesson 7-1
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 54
Answer:
The given triangle is:
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 54
From the given triangle,
We can observe that it is a right triangle
So,
Now,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the hypotenuse
a and b are the legs
Now,
8² = 4² + b²
64 = 16 + b²
b² = 64 – 16
b² = 48
b = \(\sqrt{48}\)
b = 6.9 cm
Hence, from the above,
We can conclude that the length of the unknown side is: 6.9 cm

Question 5.
The height of a shed is 6 m. A ladder leans against the shed with its base 4.5 m away, and its top just reaching the roof. What is the length of the ladder? Lesson 7-1

Answer:
It is given that
The height of a shed is 6 m. A ladder leans against the shed with its base 4.5 m away, and its top just reaching the roof.
Now,
From the given figure,
We can observe that the ladder looks like the hypotenuse of a right triangle for the shed
Now,
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the hypotenuse
a and b are the legs
In this situation,
c is the length of the ladder
a is the height of the shed
b is the length of the base
So,
c² = 6² + (4.5)²
c² = 36 + 20.25
c² = 56.25
c = \(\sqrt{56.25}\)
c = 7.5 m
Hence, from the above,
We can conclude that the length of the ladder is: 7.5 m

Question 6.
Select all the sets of lengths that could represent the sides of a right triangle. Lesson 7-2
☐ 5 cm, 10 cm, 15 cm
☐ 7 in., 14 in., 25 in.
☐ 13 m, 84 m, 85 m
☐ 5 ft, 11 ft, 12 ft
☐ 6ft, 9 ft, \(\sqrt {117}\) ft
Answer:
Let the given options be named as A, B, C, D, and E
Now,
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the hypotenuse and has the longest length
a and b are the legs
So,
A)
15² = 5² + 10²
225 = 25 + 100
225 ≠ 125
B)
25² = 7² + 14²
625 = 49 + 196
625 ≠ 245
C)
85² = 84² + 13²
7,225 = 7,056 + 169
7,225 = 7,225
D)
12² = 11² + 5²
144 = 121 + 25
144 ≠ 146
E)
(\(\sqrt{117}\))² = 6² + 9²
117 = 36 + 81
17 = 117
Hence, from the above,
We can conclude that the side lengths present in options C and E represent the side lengths of a right triangle

Topic 7 MID-TOPIC PERFORMANCE TASK

Javier is standing near a palm tree. He holds an electronic tape measure near his eyes and finds the three distances shown.

PART A
Javier says that he can now use the Pythagorean Theorem to find the height of the tree. Explain. Use vocabulary terms in your explanation.
Answer:
It is given that
Javier says that he can now use the Pythagorean Theorem to find the height of the tree
Now,
According to the Pythagorean Theorem,
In a right-angled triangle, the square of the hypotenuse side is equal to the sum of squares of the other two sides“. The sides of this triangle have been named Perpendicular (The height of the tree), Base, and Hypotenuse.

PART B
Find the height of the tree. Round to the nearest tenth. Show your work.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 55
Answer:
From the given figure,
We can observe that
To find the height of the tree, we have to find the perpendicular distances of the two right triangles
Now,
Let x be the perpendicular height of the first right triangle
Let y be the perpendicular height of the second right triangle
So,
The height of the tree = x + y
Now,
The side lengths of the first right triangle are: 25 ft, 7 ft, x ft
Now,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the hypotenuse
a and b are the side lengths
So,
25² = 7² + x²
x² = 625 – 49
x² = 576
x = \(\sqrt{576}\)
x = 24 ft
Now,
The side lengths of the second right triangle are: 9 ft, 7ft, y ft
So,
9² = 7² + y²
y² = 81 – 49
y² = 32
y = \(\sqrt{32}\)
y = 5.6 ft
So,
The height of the tree = 24 + 5.6
= 29.6 ft
Hence, from the above,
We can conclude that the height of the tree to the nearest tenth is: 29.6 ft

PART C
Javier moves backward so that his horizontal distance from the palm tree is 3 feet greater. Will the distance from his eyes to the top of the tree also be 3 feet greater? Explain.
Answer:
Yes it will be greater, he is moving back 3 feet so what you are doing is taking the leg (a²) and multiplying it by 3. Once you do, you see triangle 1 has double and so did triangle 2. Triangle 2 was originally 5.6 (rounded to 6) then went up to 26.1. Triangle 1 was originally 24 and went up to 74.7 (or 75)
Step-by-step explanation:
For Triangle 1 (when multiplied by 3):
We know that,
a² + b² = c²
7² + b² = 27²
49 + b² = 729
b² = 680
b  = \(\sqrt{680}\)
b = 26.1 ft
For Triangle 2:
We know that,
a² + b² = c²
7² + b² =75²
b² = 5576
b = \(\sqrt{5,576}\)
b = 74.7 ft

PART D
Could Javier change his horizontal distance from the tree so that the distance from his eyes to the top of the tree is only 20 feet? Explain.
Answer:
Yes, Javier can change his horizontal distance from the tree so that the distance from his eyes to the top of the tree is only 20 feet by moving forward 5 ft

Lesson 7.3 Apply the Pythagorean Theorem to Solve Problems

Solve & Discuss It!
Carlos is giving his friend in another state a new umbrella as a gift. He wants to ship the umbrella in a box he already has. Which box can Carlos use to ship the umbrella? Explain.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 56
I can… use the Pythagorean Theorem to solve problems.
Answer:
It is given that
Carlos is giving his friend in another state a new umbrella as a gift. He wants to ship the umbrella in a box he already has.
Now,
From the given figure,
We can observe that the umbrella is 37.5 inches long.
Now,
If you observe, each box doesn’t have 37 inches wide, however, they are tridimensional figures, which means they have a certain height.
So,
The smaller box is too small to fit the umbrella.
But,
The medium box is perfect because it has 27 inches wide and 27 inches in height, which is enough to fit the umbrella. These are the best dimensions to send the umbrella.
Hence, from the above,
We can conclude that the box that can be used by Carlos to ship the umbrella has the dimensions 27 in × 14 in × 27 in

Make Sense and Persevere
How will the umbrella fit inside any of the boxes?
Answer:
We know that,
The box is a 3-d figure
So,
To fit the whole umbrella in the box, we have to put it in a diagonal manner i.e., like the hypotenuse of a right triangle

Focus on math practices
Construct Arguments Tim says that the diagonal of any of the boxes will always be longer than the sides. Is Tim correct? Explain.
Answer:
We know that,
If we consider a square or any 2-d figure or any 3-d figure that consists of 1 right angle,
then, the diagonal will divide a figure into 2 right triangles
We know that,
We can apply the Pythagorean Theorem for any right triangle
We know that,
In a right triangle,
The hypotenuse is the longest side
We know that,
The hypotenuse in a right triangle is considered as a diagonal in a figure that consists of 1 right angle
Hence, from the above,
We can conclude that Tim is correct

Essential Question
What types of problems can be solved using the Pythagorean Theorem?
Answer:
The Pythagorean theorem is a way of relating the leg lengths of a right triangle to the length of the hypotenuse, which is the side opposite the right angle. Even though it is written in these terms, it can be used to find any of the sides as long as you know the lengths of the other two sides

Try It!

What is the length of the diagonal, d, of a rectangle with length 19 feet and width 17 feet?
leg2 + leg2 = hypotenuse2
______ 2 + _______2 = d2
______ + _______ = d2
_______ = d2
________ ≈ d
Answer:
It is given that a rectangle has a length of 19 feet and a width of 17 feet
Now,
We know that,
In a rectangle,
If a diagonal is drawn, then it divides the rectangle into 2 right angles
So,
According to the Pythagorean Theorem,
d² = a² + b²
Where,
d is the diagonal or hypotenuse
a and b are the lengths of the legs
So,
d²= 19² + 17²
d² = 361 + 289
d² = 650
d = \(\sqrt{650}\)
d = 25.4 ft
Hence, from the above,
We can conclude that the length of the diagonal is: 25.4 ft

Convince Me!
If the rectangle were a square, would the process of finding the length of the diagonal change? Explain.
Answer:
We know that,
For any figure i.e., either 2-d figure or 3-d figure with 1 right angle, the diagonal will divide that figure into 2 right angles
We know that,
We will use the Pythagorean Theorem to find the length of any unknown side in the right triangle
Hence, from the above,
We can conclude that even if the rectangle were a square, the process of finding the length of the diagonal will not change

Try It!

A company wants to rent a tent that has a height of at least 10 feet for an outdoor show. Should they rent the tent shown at the right? Explain.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 57
Answer:
It is given that
A company wants to rent a tent that has a height of at least 10 feet for an outdoor show.
Now,
The given figure is:
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 57
Now,
To find whether the tent should be rented or not,
We have to find the value of h
We can also observe that the triangle that contains the value of h is a right triangle
Now,
The base of the right triangle = \(\frac{24}{2}\)
= 12 ft
Now,
The side lengths of the right triangle are: h, 15 ft, 12 ft
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
So,
15² = 12² + h²
h² = 225 – 144
h² = 81
h = \(\sqrt{81}\)
h = 9 ft
But,
The given height of the tent is: 10 ft
So,
9 ft < 10 ft
Hence, from the above,
We can conclude that the company should not rent the tent

KEY CONCEPT

You can use the Pythagorean Theorem and its converse to solve problems involving right triangles.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 58

Do You Understand?
Question 1.
Essential Question What types of problems can be solved using the Pythagorean Theorem?
Answer:
The Pythagorean theorem is a way of relating the leg lengths of a right triangle to the length of the hypotenuse, which is the side opposite the right angle. Even though it is written in these terms, it can be used to find any of the sides as long as you know the lengths of the other two sides

Question 2.
Look for Structure How is using the Pythagorean Theorem in a rectangular prism similar to using it in a rectangle?
Answer:
We know that,
The rectangular prism and the rectangle have at least 1 right angle
We know that,
If a 3-d or 2-d figure has 1 right angle, then the diagonal of that figure divides the figure into the right triangles
So,
If we have the right triangle, then we can use the Pythagorean Theorem irrespective of the overall shape of the figure

Question 3.
Construct Arguments Glen found the length of the hypotenuse of a right triangle using \(\sqrt{a^{2}+b^{2}}\). Gigi used \(\sqrt{(a+b)^{2}}\). Who is correct? Explain.
Answer:
It is given that
Glen found the length of the hypotenuse of a right triangle using \(\sqrt{a^{2}+b^{2}}\). Gigi used \(\sqrt{(a+b)^{2}}\).
Now,
We know that,
We can use the Pythagorean Theorem only for the right triangles
The condition for a triangle to become the right triangle is:
Hypotenuse² = Side² + Side²
c² = a² + b²
Hence, from the above,
We can conclude that Glen is correct

Do You Know How?
Question 4.
You are painting the roof of a boathouse. You are going to place the base of a ladder 12 feet from the boathouse. How long does the ladder need to be to reach the roof of the boathouse?
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 59
Answer:
It is given that
You are painting the roof of a boathouse. You are going to place the base of a ladder 12 feet from the boathouse.
Now,
From the figure,
We can observe that the roof of a boathouse, ladder, and the base form a right triangle
So,
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the height of the boathouse
a is the length of the base
b is the length of the ladder
So,
35² = 12² + b²
b² = 1,225 – 144
b² = 1,081
b = \(\sqrt{1,081}\)
b = 32.9 ft
Hence, from the above,
We can conclude that the length of the ladder that is needed to reach the roof of the boathouse is: 32.9 ft

Question 5.
A box-shaped like a right rectangular prism measures 5 centimeters by 3 centimeters by 2 centimeters. What is the length of the interior diagonal of the prism to the nearest hundredth?
Answer:
It is given that
A box-shaped like a right rectangular prism measures 5 centimeters by 3 centimeters by 2 centimeters.
So,
The dimensions of a rectangular prism is: 5 cm × 3 cm × 2 cm
So,
The length of the rectangular prism is: 5 cm
The width of the rectangular prism is: 3 cm
The height of the rectangular prism is: 2 cm
Now,
We know that,
The length of the diagonal of the prism = \(\sqrt{Length^{2} + Width^{2} + Height^{2}}\)
So,
The length of the diagonal of the rectangular prism = \(\sqrt{5^{2} + 3^{2} + 2^{2}}\)
= \(\sqrt{25 + 9 + 4}\)
= \(\sqrt{38}\)
= 6.16 cm
Hence, from the above,
We can conclude that the length of the interior diagonal of the rectangular prism is: 6.16 cm

Question 6.
A wall 12 feet long makes a corner with a wall that is 14 feet long. The other ends of the walls are about 18.44 feet apart. Do the walls form a right angle? Explain.

Answer:
It is given that
A wall 12 feet long makes a corner with a wall that is 14 feet long. The other ends of the walls are about 18.44 feet apart
Now,
The given figure is:

From the given figure,
We can observe that the given situation forms the right triangle
Now,
We know that,
According to the Pythagorean Therem,
c² = a² + b²
So,
c² = 12² + 14²
c² = 144 + 196
c² = 340
c = \(\sqrt{340}\)
c = 18.44 feet
Hence, from the above,
We can conclude that the walls form a right angle

Practice & Problem Solving

Leveled Practice In 7 and 8, use the Pythagorean Theorem to solve.
Question 7.
You are going to use an inclined plane to lift a heavy object to the top of a shelving unit with a height of 6 feet. The base of the inclined plane is 16 feet from the shelving unit. What is the length of the inclined plane? Round to the nearest tenth of a foot.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 60
The length of the inclined plane is about ________ feet.
Answer:

Question 8.
Find the missing lengths in the rectangular prism.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 61
Answer:

Question 9.
A stainless steel patio heater is shaped like a square pyramid. The length of one side of the base is 19.8 inches. The slant height is 92.8 inches. What is the height of the heater? Round to the nearest tenth of an inch.
Answer:
It is given that
A stainless steel patio heater is shaped like a square pyramid. The length of one side of the base is 19.8 inches. The slant height is 92.8 inches
Now,
We know that,
The slant height is nothing but a length of the diagonal
Now,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the slant height
a is the length of the base of the steel patio heater
b is the height of the heater
So,
(92.8)² = (19.8)² + b²
b² = 8,611.84 – 392.04
c² = 8,219.8
c = \(\sqrt{8,219.8}\)
c = 90.6 inches
Hence, from the above,
We can conclude that the height of the heater is: 90.6 inches

Question 10.
Reasoning What is the measurement of the longest line segment in a right rectangular prism that is 16 centimeters long, 9 centimeters wide, and 7 centimeters tall? Round to the nearest tenth of a centimeter.
Answer:
It is given that
A right rectangular prism is 16 centimeters long, 9 centimeters wide, and 7 centimeters tall
So,
The dimensions of a right rectangular prism are: 16 cm × 9 cm × 7 cm
So,
The length of the right rectangular prism is: 16 cm
The width of the right rectangular prism is: 9 cm
The height of the right rectangular prism is: 7 cm
We know that,
The longest line segment in any 2-d or 3-d figure is a “Diagonal”
Now,
We know that,
The length of the diagonal of the right rectangular prism = \(\sqrt{Length^{2} + Width^{2} + Height^{2}}\)
So,
The length of the diagonal of the right rectangular prism = \(\sqrt{16^{2} + 9^{2} + 7^{2}}\)
= \(\sqrt{256 + 49 + 81}\)
= \(\sqrt{386}\)
= 19.64 cm
Hence, from the above,
We can conclude that the length of the longest line segment in the right rectangular prism is: 19.64 cm

Question 11.
Felipe is making triangles for a stained glass window. He made the design shown but wants to change it. Felipe wants to move the purple triangle to the corner. The purple piece has side lengths of 4.5 inches, 6 inches, and 7 inches. Can the purple piece be moved to the corner? Explain.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 62
Answer:
It is given that
Felipe is making triangles for a stained glass window. He made the design shown as above but wants to change it. Felipe wants to move the purple triangle to the corner. The purple piece has side lengths of 4.5 inches, 6 inches, and 7 inches.
Now,
From the given figure,
We can observe that
If the purple figure is moving to the corner, then one side of the purple figure will become a right angle
So,
Now,
We have to find whether the purple figure will be a right triangle or not if it moves to a corner
Now,
We know that,
According to the converse of the Pythagorean Theorem,
If
c² = a² + b²,
then, the triangle is a right triangle
We know that,
The hypotenuse has the longest side length
So,
7² = 4.5² + 6²
49 = 20.25 + 36
49 = 56.25
So,
The condition
c² = a² + b²
is false
Hence, from the above,
We can conclude that the purple figure should not

Question 12.
a. What is the longest poster you could fit in the box? Express your answer to the nearest tenth of an inch.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 63
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 63
From the given figure,
We can observe that there will be two longest sides for two pairs of different side lengths
we know that,
The longest side is nothing but a diagonal
Now,
The two pairs of side lengths are: (20, 12, x), and (8, 12, y)
Where,
x and y are the lengths of the longest sides
Now,
We know that
Since the figure consists of the right triangles,
According to the Pythagorean Theorem,
c² = a² + b²
So,
x² = 20² + 12²
x² = 400 + 144
x² = 544
x = \(\sqrt{544}\)
x = 23.32 in.
So,
y² = 12² + 8²
y² = 144 + 64
y² = 208
y = \(\sqrt{208}\)
y = 14.42 in.
Hence, from the above,
We can conclude that the longest poster that you can fit in the box is: 23.32 in.

b. Explain why you can fit only one maximum-length poster in the box, but you can fit multiple 21.5-inch posters in the same box.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 64
Answer:
It is given that
you can fit multiple 21.5-inch posters in the same box.
Now,
From part (a),
We can observe that the length of the longest poster that can fit into the box is: 23.32 in.
So,
21.5 in. < 23.32 in.
Hence, from the above,
We can conclude that since the given size of the posters is less than the maximum length of the poster,
We can fit multiple 21.5-inch posters in the same box instead of 1 poster that is of the maximum length

Question 13.

The corner of a room where two walls meet the floor should be at a right angle. Jeff makes a mark along each wall. One mark is 3 inches from the corner. The other is 4 inches from the corner. How can Jeff use the Pythagorean Theorem to see if the walls form a right angle?
Answer:
It is given that
The corner of a room where two walls meet the floor should be at a right angle. Jeff makes a mark along each wall. One mark is 3 inches from the corner. The other is 4 inches from the corner.
Now,
To see whether the walls form a right angle or not,
We have to see whether the length along the walls is greater than the lengths of the marks from the corners
Now,
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the length along the walls
a is the length of one mark from the corner
b is the length of another mark from the corner
So,
c² = 3² + 4²
c² = 9 + 16
c² = 25
c = \(\sqrt{25}\)
c = 5
So,
From the above value,
We can observe that
c > a and c > b
Hence, from the above,
We can conclude that the walls form a right angle

Question 14.
Higher-Order Thinking It is recommended that a ramp have at least 6 feet of horizontal distance for every 1 foot of vertical rise along an incline. The ramp shown has a vertical rise of 2 feet. Does the ramp show match the recommended specifications? Explain.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 65
Answer:
It is given that
It is recommended that a ramp have at least 6 feet of horizontal distance for every 1 foot of vertical rise along an incline. The ramp shown has a vertical rise of 2 feet
Now,
6 feet of horizontal distance for every 1 foot,
The ramp shown has a vertical rise of 5 feet.
So,
The rate of change (m)  ≤ \(\frac{1 foot}{6 feet}\)
Convert both to a single unit of inches
We know that,
1 foot = 12 inches
So,
m ≤ \(\frac{12 inches}{72 inches}\)
Divide by 4 into both sides
m ≤ \(\frac{4 inches}{18 inches}\)
Now,
For a ramp that has a vertical distance of 2 feet and the same horizontal distance
m = \(\frac{12 inches}{24 inches}\)
m = \(\frac{4 inches}{6 inches}\)
So,
The rate of change when the vertical distance is 6 feet > The rate of change when the vertical distance is 2 feet
Hence, from the above,
We can conclude that the ramp shown above matched the given specifications

Assessment Practice

Question 15.
A machine in a factory cuts out triangular sheets of metal. Which of the triangles are right triangles? Select all that apply.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 66
☐ Triangle 1
☐ Triangle 2
☐ Triangle 3
☐ Triangle 4
Answer:
It is given that
A machine in a factory cuts out triangular sheets of metal.
Now,
According to the converse of the Pythagorean Theorem,
If
c² = a² + b²
then, the triangle is a right triangle
Now,
For Triangle 1,
(\(\sqrt{505}\))² = 12² + 19²
505 = 505
For Triangle 2,
(\(\sqrt{467}\))² = 16² + 19²
467 ≠ 617
For Triangle 3,
(\(\sqrt{596}\))² = 14² + 20²
596 = 596
For Triangle 4,
(\(\sqrt{421}\))² = 11² + 23²
421 ≠ 650
Hence, from the above,
We can conclude that Triangle 1 and Triangle 3 are the right triangles

Question 16.
What is the length b, in feet, of the rectangular plot of land shown?
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 67
Answer:
It is given that the given figure is a rectangular plot of land
We know that,
In a rectangle,
The opposite sides are equal and the angles are all 90°
So,
A diagonal forms 2 right triangles in a rectangle
Now,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the length of the diagonal
a is the width
b is the length
Now,
325² = 300² + b²
b²= 1,05,625 – 90,000
b² = 15,625
b = \(\sqrt{15,625}\)
b = 125 ft
Hence, from the above,
We can conclude that the length of b is: 125 ft

Lesson 7.4 Find Distance in the Coordinate

Explore It!
Thomas and Jim are outside the haunted castle ride and want to get to the clown tent in time for the next show.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 68
I can… use the Pythagorean Theorem to find the distance between two points in the coordinate plane.

A. How can you represent the starred locations on a coordinate plane?
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 69
Answer:
It is given that
Thomas and Jim are outside the haunted castle ride and want to get to the clown tent in time for the next show.
Now,
The given route of the castle is:
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 68
Now,
From the given figure,
To represent the route in the coordinate plane,
The given scale is:
X-axis: 1 cm = 500 feet
Y-axis: 1 cm = 500 feet
Now,
From the given figure,
The coordinates of the starred locations can be:
The coordinates of the haunted house are: (500, 1,500),
The coordinates of the clown tent are: (2,000, 500)
Hence,
The representation of the starred locations in the coordinate plane is:

B. Jim says that the marked yellow paths show the shortest path to the tent. Write an expression to represent this and find the distance Jim walks from the haunted mansion to the clown tent.
Answer:
From part (a),
We know that,
The coordinates of the haunted house are: (500, 1,500),
The coordinates of the clown tent are: (2,000, 500)
Now,
We know that
The linear equation in the slope-intercept form is:
y = mx + b
Where,
m is the slope
b is the initial value (or) y-intercept
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
Slope (m) = y2 – y1 / x2 – x1
So,
Slope (m) = \(\frac{500 – 1,500}{2,000 – 500}\)
Slope (m) = –\(\frac{1,000}{1,500}\)
Slope (m) = –\(\frac{2}{3}\)
So,
The equation in the slope-intercept form is:
y = –\(\frac{2}{3}\)x + b
So,
3y = -2x + 3b
Now,
Substitute (500, 1,500) or (2,000, 500) in the above equation
So,
1,500 = -4000 + 3b
3b = 5,500
So,
The equation that represents the shortest path to the tent is:
3y = -2x + 5,500
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the haunted mansion and the clown tent = \(\sqrt{(2,000 – 500)^{2} + (500 – 1,500)^{2}}\)
= \(\sqrt{1,500^{2} + 1,000^{2}}\)
= \(\sqrt{2,250,000 + 1,000,000}\)
= 1,802.77 feet
Hence, from the above,
We can conclude that
The equation that represents the shortest path to the clown tent is:
3y = -2x + 5,500
The distance between the haunted mansion and the clown tent is: 1,802.77 feet

Focus on math practices
Construct Arguments Why is the distance between two nonhorizontal and nonvertical points always greater than the horizontal or vertical distance?
Answer:
Let us consider a coordinate plane
Now,
When we draw either a horizontal line or the vertical line,
We can observe that the length will be constant
But,
When we draw non-vertical and non-horizontal lines,
We can observe that the lengths are unknown and not constant
Hence, from the above,
We can conclude that the distance between two nonhorizontal and nonvertical points always greater than the horizontal or vertical distance

Essential Question
How can you use the Pythagorean Theorem to find the distance between two points?
Answer:
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the hypotenuse
a and b are the side lengths or lengths of the legs
Now,
Graphically,
The terms of the Pythagorean Theorem can be expressed as:
c is the distance between two points
a and b are the points
So,
c = \(\sqrt{a^{2} + b^{2}}\)

Try It!

What is the distance between points A and B?
The distance between point A and point B is about ________ units.
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 70
Answer:
The given graph is:
Envision Math Common Core 8th Grade Answers Topic 7 Understand And Apply The Pythagorean Theorem 70
The representation of the graph in the coordinate plane is:

From the given graph,
The coordinates of A are: (2, 3)
The coordinates of B are: (4, 1)
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the points A and B = \(\sqrt{(4 – 2)^{2} + (1 – 3)^{2}}\)
= \(\sqrt{2^{2} + 2^{2}}\)
= \(\sqrt{4 + 4}\)
= 2.83 units
Hence, from the above,
We can conclude that the distance between points A and B is about 2.83 units

Convince Me!
Why do you need to use the Pythagorean Theorem to find the distance between points A and B?
Answer:
The representation of points A and B in the coordinate plane are:

Now,
When we observe the graph,
We can see that A and B can form a right triangle
Now,
We know that,
The Pythagorean Theorem is only applicable to the right triangles
So,
According to the Pythagorean Theorem,
c² = a² + b²
c = \(\sqrt{a^{2} + b^{2}}\)
where,
c is the distance between points A and B
A and B are the given points

Try It!
Find the perimeter of ∆ABC with vertices (2, 5), (5, -1), and (2, -1).
Answer:
It is given that
∆ABC with vertices (2, 5), (5, -1), and (2, -1)
Now,
The names of the vertices are:
A (2, 5), B (5, -1), and C (2, -1)
We know that,
The perimeter of a triangle is the sum of all the side lengths of a triangle
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
In ∆ABC,
AB and BC are the side lengths
Ac is the hypotenuse
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the points A and B = \(\sqrt{(5 – 2)^{2} + (-1 – 5)^{2}}\)
= \(\sqrt{3^{2} + 6^{2}}\)
= \(\sqrt{9 + 36}\)
= 6.70 units
The distance between the points B and C (BC) = \(\sqrt{(2 – 5)^{2} + (-1 + 1)^{2}}\)
= \(\sqrt{3^{2} + 0^{2}}\)
= \(\sqrt{9 + 0}\)
= 3 units
The distance between the points A and C (AC) = \(\sqrt{(2 – 2)^{2} + (-1 – 5)^{2}}\)
= \(\sqrt{0^{2} + 6^{2}}\)
= \(\sqrt{0 + 36}\)
= 6 units
So,
The perimeter of ∆ABC = AB + BC + AC
= 6 + 3 + 6.70
= 15.7 units
Hence, from the above,
We can conclude that the perimeter of ∆ABC is about 15.7 units

Try It!

What are the coordinates, to the nearest tenth, of the third vertex in an isosceles triangle that has one side length of 2 and two side lengths of 5, with vertices at (1, 0) and (1, 2)? The third vertex is in the first quadrant.
Answer:
It is given that
An isosceles triangle that has one side length of 2 and two side lengths of 5, with vertices at (1, 0) and (1, 2)
Now,
Let the third vertex be (x, y)
Now,
The given vertices are:
A (1, 0), B (1, 2), and C (x, y)
It is also given that
BC = 2 units, and AC = 5 units
We know that,
An isosceles triangle has any 2 equal side lengths
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the points A and B = \(\sqrt{(2 – 0)^{2} + (1 – 1)^{2}}\)
= \(\sqrt{2^{2} + 0^{2}}\)
= \(\sqrt{4 + 0}\)
= 4 units
The distance between the points B and C = \(\sqrt{(x – 1)^{2} + (y – 2)^{2}}\)
Squaring on both sides
So,
BC² = (x – 1)² + (y – 2)²
The distance between the points A and C = \(\sqrt{(x – 1)^{2} + (y – 0)^{2}}\)
Squaring on both sides
So,
BC² = (x – 1)² + y²
So,
(x – 1)² + (y – 2)² = 4 —– (1)
(x – 1)² + y² = 25 —— (2)
So,
From eq (1) and eq (2),
25 – y² + (y – 2)² = 4
-y² + y² – 4y + 4 = -21
-4y = -25
y = \(\frac{25}{4}\)
So,
(x – 1)² = |25 – (\(\frac{25}{4}\))²|
x = \(\frac{19}{4}\)
Hence, from the above,
We can conclude that the third vertex is: (\(\frac{19}{4}\), \(\frac{25}{4}\))

KEY CONCEPT

You can use the Pythagorean Theorem to find the distance between any two points, P and Q, on the coordinate plane.
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 71

Do You Understand?
Question 1.
Essential Question How can you use the Pythagorean Theorem to find the distance between two points?
Answer:
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the hypotenuse
a and b are the side lengths or lengths of the legs
Now,
Graphically,
The terms of the Pythagorean Theorem can be expressed as:
c is the distance between two points
a and b are the points
So,
c = \(\sqrt{a^{2} + b^{2}}\)

Question 2.
Model with Math
Can you use a right triangle to represent the distance between any two points on the coordinate plane? Explain.
Answer:
Derived from the Pythagorean Theorem, the distance formula is used to find the distance between two points in the plane. We know that,
According to the Pythagorean Theorem,
a²+b²=c²
where,
a and b are the lengths of the legs adjacent to the right angle
c is the length of the hypotenuse.

Question 3.
Generalize How does the fact that the points are on opposite sides of the y-axis affect the process of finding the distance between the two points?
Answer:
The fact that the points are on opposite sides of the y-axis affects the process of finding the distance between the two points because  We need to find the distance between the two points by adding the distances from each of them to the y-axis.

Do You Know How?
In 4-6, use the coordinate plane below.
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 72
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 72
From the given coordinate plane,
The given points are:
C (1, 2), D (2, -1), and E (-2, 1)

Question 4.
Find the distance between points C and D. Round to the nearest hundredth.
Answer:
Compare the points C and D with (x1, y1), (x2, y2)
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the points C and D = \(\sqrt{(2 – 1)^{2} + (-1 – 2)^{2}}\)
= \(\sqrt{1^{2} + 3^{2}}\)
= \(\sqrt{1 + 9}\)
= 3.16 units
Hence, from the above,
We can conclude that the distance between points C and D is: 3.16 units

Question 5.
Find the perimeter of ∆CDE.
Answer:
We know that,
The “Perimeter” is defined as the sum of all the side lengths
So,
The perimeter of ∆CDE = CD + DE + CE
So,
The distance between the points C and D = \(\sqrt{(2 – 1)^{2} + (-1 – 2)^{2}}\)
= \(\sqrt{1^{2} + 3^{2}}\)
= \(\sqrt{1 + 9}\)
= 3.16 units
The distance between the points D and E = \(\sqrt{(-2 – 2)^{2} + (1 + 1)^{2}}\)
= \(\sqrt{4^{2} + 2^{2}}\)
= \(\sqrt{16 + 4}\)
= 4.47 units
The distance between the points C and E = \(\sqrt{(-2 – 1)^{2} + (1 – 2)^{2}}\)
= \(\sqrt{3^{2} + 1^{2}}\)
= \(\sqrt{1 + 9}\)
= 3.16 units
So,
The perimeter of ∆CDE = 3.16 + 4.47 + 3.16
= 10.79 units
Hence, from the above,
We can conclude that the perimeter of ∆CDE is: 10.79 units

Question 6.
Point B is plotted on the coordinate plane above the x-axis. ∆BDE is equilateral. What are the coordinates of point B to the nearest hundredth?
Answer:
It is given that
Point B is plotted on the coordinate plane above the x-axis. ∆BDE is equilateral.
Now,
Let the unknown vertex be B (x, y)
So,
The given points are:
B (x, y), D (2, -1), and E (-2, 1)
It is given that ΔBDE is equilateral
So,
BD = DE = EB
BD² = DE² = EB²
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the points B and D = \(\sqrt{(x – 2)^{2} + (y – 1)^{2}}\)
Squaring on both sides
So,
BD² = (x – 2)² + (y + 1)²
The distance between the points D and E = \(\sqrt{(1 + 1)^{2} + (-2 – 2)^{2}}\)
= \(\sqrt{2^{2} + 4^{2}}\)
= \(\sqrt{4 + 16}\)
= 4.47 units
The distance between the points E and B = \(\sqrt{(x + 2)^{2} + (y – 1)^{2}}\)
Squaring on both sides
So,
EB² = (x + 2)² + (y – 1)²
Now,
(x – 2)² + (y + 1)² = 4.47 —- (1)
(x + 2)² + (y – 1)² = (x – 2)² + (y + 1)²
x² + 2x + 4 + y² + 1 – 2y = x² + 4 – 4x + y² + 1 + 2y
2x + 4 + 1 – 2y = 4 – 4x + 1 + 2y
6x + 5 = 4y + 5
6x = 4y
3x = 2y
x = \(\frac{2}{3}\)y
Now,
From eq (1),
x² + 4 – 4x + y² + 1 + 2y = 4.47
x² + y² -4x + 2y = -0.47
(\(\frac{2}{3}\)y)² + y² – 4 (\(\frac{2}{3}\))y + 2y = -0.47
4y² + 15y + 4.23 = 0
So,
y = -0.30 (or) y = -3.44
So,
x = \(\frac{2}{3}\) (-0.30) (or) x = \(\frac{2}{3}\) (-3.44)
x = -0.2 (or) x = -2.29
Hence, from the above,
We can conclude that the coordinates of point B are: (-0.2, -0.30) or (-2.29, -3.44)

Practice & Problem Solving

Question 7.
Leveled Practice Use the Pythagorean Theorem to find the distance between points P and Q.
Label the length, in units, of each leg of the right triangle.
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 73
The distance between point P and point Q is __________ units.
Answer:
From the given coordinate plane,
There are only 2 vertices
Let the third vertex be R(x, y) and the coordinates of R can be found from the coordinate plane
Now,
From the given coordinate plane,
The vertices are:
P (3, 2), Q (9, 10), and R (9, 2)
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the points Q and R = \(\sqrt{(9 – 9)^{2} + (10 – 2)^{2}}\)
= \(\sqrt{0^{2} + 8^{2}}\)
= \(\sqrt{0 + 64}\)
= 8 units
The distance between the points P and R = \(\sqrt{(9 – 3)^{2} + (2 – 2)^{2}}\)
= \(\sqrt{0^{2} + 6^{2}}\)
= \(\sqrt{0 + 36}\)
= 6 units
Now,
From the given coordinate plane,
We can observe that P, Q, R form the right triangle
So,
According to the Pythagorean Theorem,
PQ² = QR² + PR²
PQ² = 8² + 6²
PQ² = 64 + 36
PQ² = 100
PQ = \(\sqrt{100}\)
PQ = 10 units
Hence, from the above,
We can conclude that the length of PQ is: 10 units

Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 74
Question 8.
Find the perimeter of triangle QPR. Round to the nearest hundredth.
Answer:
From the coordinate plane,
The vertices of ΔPQR are:
P (-5, -2), Q (2, -2), and R (-1, 3)
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the points P and Q = \(\sqrt{(2 + 5)^{2} + (2 – 2)^{2}}\)
= \(\sqrt{0^{2} + 7^{2}}\)
= \(\sqrt{0 + 49}\)
= 7 units
The distance between the points Q and R = \(\sqrt{(-1 – 2)^{2} + (3 + 2)^{2}}\)
= \(\sqrt{3^{2} + 5^{2}}\)
= \(\sqrt{9 + 25}\)
= 5.83 units
The distance between the points P and R = \(\sqrt{(1 – 5)^{2} + (-3 – 2)^{2}}\)
= \(\sqrt{4^{2} + 5^{2}}\)
= \(\sqrt{16 + 25}\)
= 6.40 units
So,
The perimeter of ΔPQR = PQ + QR + PR
= 7 + 5.83 + 6.40
= 19.23 units
Hence, from the above,
We can conclude that the perimeter of ΔPQR is: 19.23 units

Question 9.
Determine whether the triangle is equilateral, isosceles, or scalene.
Answer:
We know that,
On the basis of the side lengths,
Scalene Triangle – All the side lengths are different
Equilateral Triangle – All the side lengths are the same
Isosceles Triangle – Any two of the side lengths are the same
So,
From Exercise 8,
We can observe that all the side lengths are different
Hence, from the above,
We can conclude that ΔPQR is a scalene Triangle

Question 10.
You walk along the outside of a park starting at point P. Then you take a shortcut represented by \(\overline{P Q}\) on the graph.
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 75
a. What is the length of the shortcut in meters? Round to the nearest tenth of a meter.
Answer:
It is given that
You walk along the outside of a park starting at point P. Then you take a shortcut represented by \(\overline{P Q}\) on the graph.
Now,
From the given figure,
We can observe that
The vertices are:
P (0, 0), Q (40, 85), and R (40, 0)
The shortest path is represented as PQ
Now,
Compare the points P and Q with (x1, y1), (x2, y2)
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the points P and Q = \(\sqrt{(40 – 0)^{2} + (85 – 0)^{2}}\)
= \(\sqrt{40^{2} + 85^{2}}\)
= \(\sqrt{1,600 + 7,225}\)
= 93.9 m
Hence, from the above,
We can conclude that the length of the shortest path is: 93.9 meters

b. What is the total length of your walk in the park? Round to the nearest tenth of a meter.
Answer:
We know that,
The total length is nothing but the “Perimeter”
So,
The perimeter of the given triangle = PQ + QR + PR
Now,
The distance between the points P and Q = \(\sqrt{(40 – 0)^{2} + (85 – 0)^{2}}\)
= \(\sqrt{40^{2} + 85^{2}}\)
= \(\sqrt{1,600 + 7,225}\)
= 93.9 m
The distance between the points Q and R = \(\sqrt{(40 – 40)^{2} + (85 – 0)^{2}}\)
= \(\sqrt{0^{2} + 85^{2}}\)
= \(\sqrt{0 + 7,225}\)
= 85 m
The distance between the points P and R = \(\sqrt{(40 – 0)^{2} + (0 – 0)^{2}}\)
= \(\sqrt{0^{2} + 40^{2}}\)
= \(\sqrt{0 + 1,600}\)
= 40 m
So,
The total length of your walk in the park = PQ + QR + PR
= 93.9 + 85 + 40
= 218.9 meters
Hence, from the above,
We can conclude that the total length of your walk in the park is: 218.9 meters

Question 11.
Suppose a park is located 3.6 miles east of your home. The library is 4.8 miles north of the park. What is the shortest distance between your home and the library?
Answer:
It is given that
A park is located 3.6 miles east of your home. The library is 4.8 miles north of the park
So,
The representation of the above situation is:

Now,
According to the Pythagorean Theorem,
(The shortest distance between home and library)² = (The distance from home to park)² + (he distance from park to library)²
(The shortest distance between home and library)² = 3.6² + 4.8²
(The shortest distance between home and library)² = 12.96 + 23.04
The shortest distance between home and library = 6
Hence, from the above,
We can conclude that the shortest distance between home and library is: 6 miles

Question 12.
Use Structure Point B has coordinates (2, 1). The x-coordinate of point A is -10. The distance between point A and point B is 15 units. What are the possible coordinates of point A?
Answer:
It is given that
Point B has coordinates (2, 1). The x-coordinate of point A is -10. The distance between point A and point B is 15 units
Now,
Let the coordinates of A be:
(x, y) = (-10, y)
Now,
Compare the points A and B with (x1, y1), (x2, y2)
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the points A and B = \(\sqrt{(-10 – 2)^{2} + (y – 1)^{2}}\)
15 = \(\sqrt{12^{2} + (y – 1)^{2}}\)
15 = \(\sqrt{144 + (y – 1)^{2}}\)
Now,
Squaring on both sides
So,
144 + (y – 1)² = 225
(y  1)² = 225 – 144
(y – 1)² = 81
y – 1 = \(\sqrt{81}\)
y – 1 = 9 (or) y – 1 = -9
y = 9 + 1 (or) y = -9 + 1
y = 10 (or) y = -8
Hence, from the above,
We can conclude that the possible coordinates of A are: (-10, 10), and (-10, -8)

Question 13.
Higher-Order Thinking ∆EFG and ∆HIJ have the same perimeter and side lengths. The coordinates are E(6, 2), F(9, 2), G(8, 7), H(0, 0), and I(0, 3). What are the possible coordinates of point J?
Answer:
It is given that
∆EFG and ∆HIJ have the same perimeter and side lengths. The coordinates are E(6, 2), F(9, 2), G(8, 7), H(0, 0), and I(0, 3)
So,
According to the side lengths,
EF = HI, FG = IJ, and GE = JH
So,
EF² = HI², FG²= JI², and GE² = JH²
Now,
Let the unknown vertex be J (x, y)
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the points E and F = \(\sqrt{(9 – 6)^{2} + (2 – 2)^{2}}\)
= \(\sqrt{3^{2} + 0^{2}}\)
= \(\sqrt{9 + 0}\)
= 3 units
The distance between the points F and G = \(\sqrt{(8 – 9)^{2} + (7 – 2)^{2}}\)
= \(\sqrt{1^{2} + 5^{2}}\)
= \(\sqrt{1 + 25}\)
= 5.09 units
The distance between the points G and E = \(\sqrt{(8 – 6)^{2} + (7 – 2)^{2}}\)
= \(\sqrt{2^{2} + 5^{2}}\)
= \(\sqrt{4 + 25}\)
= 5.38 units
Now,
The distance between the points H and I = \(\sqrt{(0 – 0)^{2} + (3 – 0)^{2}}\)
= \(\sqrt{3^{2} + 0^{2}}\)
= \(\sqrt{9 + 0}\)
= 3 units
The distance between the points I and J = \(\sqrt{(x – 0)^{2} + (y – 3)^{2}}\)
5.09 = \(\sqrt{x^{2} + (y – 3)^{2}}\)
Squaring on both sides
So,
x² + (y – 3)² = 25.90 units
The distance between the points J and H = \(\sqrt{(x – 0)^{2} + (y – 0)^{2}}\)
5.38 = \(\sqrt{x^{2} + y^{2}}\)
Squaring on both sides
So,
x² + y² = 28.94 units
Now,
28.94 – y² + (y – 3)² = 25.90
y² + 9 – 6y – y² = 25.90 – 28.94
9 – 6y = -3.04
-6y = -3.04 – 9
6y = 12.04
y = 2
Now,
Substitute the value of y in eq 2
x² + 4 = 28.94
x² = 24.94
x = 4.99 (or) x = -4.99
Hence, from the baove,
We can conclude that the missing vertex is: J (4.99, 2) or J (-4.99, 2)

b. Explain why there can be different possibilities for the coordinates for point J.
Answer:

Assessment Practice
Question 14.
Find the distance, in units, between P and R. Round to the nearest tenth.
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 76
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 76
From the given coordinate plane,
The points are:
P (5, 10), and R (12, 14)
Now,
Compare the points P and R with (x1, y1), (x2, y2)
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the points P and R = \(\sqrt{(14 – 10)^{2} + (12 – 5)^{2}}\)
= \(\sqrt{4^{2} + 7^{2}}\)
= \(\sqrt{16 + 49}\)
= 8.1 units
Hence, from the above,
We can conclude that the distance between P and R is: 8.1 units

Question 15.
Find the distance, in units, between A(1, 5) and B(5.5, 9.25). Round to the nearest tenth.
Answer:
The given points are:
A (1, 5), and B (5.5, 9.25)
Now,
Compare the points A and B with (x1, y1), (x2, y2)
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the points A and B = \(\sqrt{(9.25 – 5)^{2} + (5.5 – 1)^{2}}\)
= \(\sqrt{4.25^{2} + 4.5^{2}}\)
= \(\sqrt{18.06 + 20.25}\)
= 6.2 units
Hence, from the above,
We can conclude that the distance between points A and B is: 6.2 units

Topic 7 REVIEW

Topic Essential Question
How can you use the Pythagorean Theorem to solve problems?
Answer:
Step 1:
Draw a right triangle and then read through the problems again to determine the length of the legs and the hypotenuse. Step 2:
Use the Pythagorean Theorem (a2 + b2 = c2) to write an equation to be solved.
Step 3:
Simplify the equation by distributing and combining like terms as needed.

Vocabulary Review

Complete each definition and then provide an example of each vocabulary word.
Vocabulary
The converse of the Pythagorean Theorem
hypotenuse
leg
proof
Pythagorean Theorem

Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 77
Answer:

Use Vocabulary in Writing
All faces of the figure are rectangles. Explain how to find the length of d. Use vocabulary terms in your description.
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 78
Answer:
The given figure is:
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 78
From the given figure,
We can observe that there are 2 right triangles
Now,
For the first right triangle,
The given side lengths are:
a = 3, b = 4, and c = x
Now,
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
So,
x² = 3² + 4²
x² = 9 + 16
x² = 25
x = \(\sqrt{25}\)
x = 5
Now,
For the second right triangle,
a = 5, b = 12, and c = d
So,
d² = 5² + 12²
d² = 25 + 144
d² = 169
d = \(\sqrt{169}\)
d = 13
Hence, from the above,
We can conclude that the length of d is: 13 units

Concepts and Skills Review

Lesson 7.1 Understand the Pythagorean Theorem

Quick Review
The Pythagorean Theorem states that, in a right triangle, the sum of the squares of the lengths of the legs, a and b, is equal to the square of the length of the hypotenuse, c. So, a2 + b2 = c2.

Example
Find the length of the hypotenuse of a triangle with legs of 7 meters and 24 meters.
Answer:
Substitute 7 for a and 24 for b. Then solve for c.
a2 + b2 = c2
49 + 576 = c2
\(\sqrt {625}\) = C
The length of the hypotenuse is 25 meters.

Practice
Question 1.
Find the length of the hypotenuse.
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 79
Answer:
The given right triangle is:
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 79
Now,
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the hypotenuse
a and b are the side lengths
So,
c² = 12² + 5²
c² = 144 + 25
c² = 169
c = \(\sqrt{169}\)
c = 13
Hence, from the above,
We can conclude that the length of the hypotenuse is: 13 cm

Question 2.
Find the unknown side length. Round to the nearest tenth.
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 80
Answer:
The given right triangle is:
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 80
Now,
We know that,
According to the Pythagorean Theorem,
c² = a² + b²
Where,
c is the hypotenuse
a and b are the side lengths
So,
9² = 7² + b²
b² = 81 – 49
b² = 32
b = \(\sqrt{32}\)
b = 5.65
Hence, from the above,
We can conclude that the length of the hypotenuse is: 5.65 in.

Lesson 7.2 Understand the Converse of the Pythagorean Theorem

Quick Review
For a triangle with side lengths a, b, and c, if a2 + b2 = c2, then the triangle is a right triangle by the Converse of the Pythagorean Theorem.

Example
Is a triangle with side lengths of 8 m, 15 m, and 17 m a right triangle? Explain.
Answer:
Substitute 8 for a, 15 for b, and 17 for c.
a2 + b2 \(\underline{\underline{?}}\) c2
82 + 152 \(\underline{\underline{?}}\) 172
289 = 289 ✓
Because a2 + b2 = c2, the triangle is a right triangle.

Practice
Question 1.
Is the triangle a right triangle? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 81
Answer:
The given triangle is:
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 81
Now,
We know that,
According to the converse of the Pythagorean Theorem,
If
c² = a² + b²
then, the given triangle is a right triangle
So,
Now,
37² = 35² + 12²
1,369 = 1,225 + 144
1,369 = 1,369
So,
The condition c² = a² + b² is true
Hence, from the above,
We can conclude that the given triangle is a right triangle

Question 2.
A triangle has side lengths of 1.5 inches, 2 inches, and 3 inches. Is the triangle a right triangle? Explain.
Answer:
It is given that
A triangle has side lengths of 1.5 inches, 2 inches, and 3 inches
Now,
We know that,
According to the converse of the Pythagorean Theorem,
If
c² = a² + b²
then, the given triangle is a right triangle
We know that,
The longest side is the hypotenuse
So,
Now,
3² = (1.5)² + 2²
9 = 2.25 + 4
9 = 6.25
So,
The condition c² = a² + b² is false
Hence, from the above,
We can conclude that the given triangle is not a right triangle

Question 3.
A triangle has side lengths of 9 feet, 40 feet, and 41 feet. Is the triangle a right triangle? Explain
Answer:
It is given that
A triangle has side lengths of 9 feet, 40 feet, and 41 feet
Now,
We know that,
According to the converse of the Pythagorean Theorem,
If
c² = a² + b²
then, the given triangle is a right triangle
We know that,
The longest side is the hypotenuse
So,
Now,
41² = 40² + 9²
1,681 = 1,600 + 81
1,681 = 1,681
So,
The condition c² = a² + b² is true
Hence, from the above,
We can conclude that the given triangle is a right triangle

Lesson 7.3 Apply the Pythagorean Theorem to Solve Problems

Quick Review
The Pythagorean Theorem can be used to find unknown side lengths of an object that is shaped like a right triangle. It also can be used to find diagonal measures in certain two-dimensional and three-dimensional objects.

Example
A shipping box is 20 inches long along the diagonal of its base. Each diagonal of the box is 29 inches long. How tall is the box?
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 82
Answer:
Substitute 20 for a and 29 for c. Then solve for b.
a2 + b2 = c2
202 + b2 = 292
400 + b2 = 841
b = \(\sqrt {441}\)
The height of the shipping box is 21 inches.

Practice
Question 1.
A basketball court is in the shape of a rectangle that is 94 feet long and 50 feet wide. What is the length of a diagonal of the court? Round to the nearest tenth.
Answer:
It is given that
A basketball court is in the shape of a rectangle that is 94 feet long and 50 feet wide
We know that,
By drawing a diagonal in the rectangle, it will become 2 right triangles
The diagonal will be the hypotenuse of the right triangle
Now,
We know that,
According to the Pythagorean Theorem,
c² = a²+ b²
Where,
c is the length of the diagonal
a and b are the side lengths
So,
c² = 94²+ 50²
c²= 8,836 + 2,500
c² = 11,336
c = \(\sqrt{11,336}\)
c = 106.4 feet
hence, from the above,
We can conclude that the length of the diagonal is: 106.4 feet

Question 2.
A packaging box for a metal rod is 7.5 inches along a diagonal of the base. The height of the box is 18 inches. What is the length of a diagonal of the box?
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 83
Answer:
It is given that
A packaging box for a metal rod is 7.5 inches along a diagonal of the base. The height of the box is 18 inches.
Now,
From the given figure,
We can observe that it looks like a right triangle
Now,
We know that,
According to the Pythagorean Theorem,
c² = a²+ b²
Where,
c is the length of the diagonal
a and b are the side lengths
So,
c² = 18² + (7.5)²
c²= 324 + 56.25
c² = 380.25
c = \(\sqrt{380.25}\)
c = 19.5 inches
Hence, from the above,
We can conclude that the length of the diagonal of the box is: 19.5 inches

Lesson 7.4 Find Distance in the Coordinate Plane

Quick Review
The Pythagorean Theorem can be used to find the distance between any two points on the coordinate plane.

Example
Find the distance between the two points on the coordinate plane. Round to the nearest tenth.
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 84
Answer:
Draw a right triangle. Determine the lengths of its legs.
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 85
The length of the horizontal leg is 5 units.
The length of the vertical leg is 5 units.
Use the relationship a2 + b2 = c2. Substitute 5 for a and 5 for b. Then solve for C.
a2 + b2 = -2
52 + 52 = c2
25 + 25 = c2
50 = c2
\(\sqrt {50}\) = C
7.1 ≈ c
The distance between the two points is about 7.1 units.

Practice
Question 1.
Points C and D represent the location of two parks on a map. Find the distance between the parks if the length of each unit on the grid is equal to 25 miles. Round to the nearest mile.
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 86
Answer:
It is given that
Points C and D represent the location of two parks on a map
Now,
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 86
From the given coordinate plane,
The points are:
C (-2, 2), and D (4, -1)
Now,
Compare the points C and D with (x1, y1), (x2, y2)
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the points C and D = \(\sqrt{(-1 – 2)^{2} + (4 + 2)^{2}}\)
= \(\sqrt{3^{2} + 6^{2}}\)
= \(\sqrt{9 + 36}\)
= 6.70 units
It is given that the length of each unit in the grid is: 25 miles
So,
The distance between the points C and D = 6.25 × 25
= 156.25 miles
Hence, from the above,
We can conclude that the distance between points C and D is: 156.25 miles

Question 2.
Find the perimeter of ∆ABC. Round to the nearest tenth.
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 87
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 87
Now,
From the given coordinate plane,
The vertices of ΔABC are:
A (1, 2), B (7, 9), and C (7, 2)
We know that,
The perimeter of a triangle is the sum of all the side lengths of a triangle
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
From the given coordinate plane,
We know that,
In ∆ABC,
AC and BC are the side lengths
AB is the hypotenuse
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the points A and C = \(\sqrt{(2 – 2)^{2} + (7 – 1)^{2}}\)
= \(\sqrt{0^{2} + 6^{2}}\)
= \(\sqrt{36 + 0}\)
= 6 units
The distance between the points B and C (BC) = \(\sqrt{(7 – 7)^{2} + (-2 + 9)^{2}}\)
= \(\sqrt{0^{2} + 7^{2}}\)
= \(\sqrt{0 + 49}\)
= 7 units
The distance between the points A and B (AB) = \(\sqrt{(9 – 2)^{2} + (7 – 1)^{2}}\)
= \(\sqrt{7^{2} + 6^{2}}\)
= \(\sqrt{49 + 36}\)
= 9.21 units
So,
The perimeter of ∆ABC = AB + BC + AC
= 6 + 7 + 9.21
= 22.2 units
Hence, from the above,
We can conclude that the perimeter of ∆ABC is about 22.2 units

Question 3.
Triangle JKL is an equilateral triangle with two of its vertices at points J and K. What are the coordinates of point L? Round to the nearest tenth as needed.
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 88
Answer:
It is given that
Triangle JKL is an equilateral triangle with two of its vertices at points J and K
Now,
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 88
Now,
From the given coordinate plane,
The two vertices of ΔJKL are:
J (3, 2), K (9, 2)
Now,
Let the third vertex be L (x, y)
We know that,
In an equilateral triangle, all the side lengths are the same
So,
JK = KL = JL
JK² = KL² = JL²
So,
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
The distance between two points = √(x2–  x1) + (y2 – y1
So,
The distance between the points J and K = \(\sqrt{(9 – 3)^{2} + (2 – 2)^{2}}\)
= \(\sqrt{0^{2} + 6^{2}}\)
= \(\sqrt{36 + 0}\)
= 6 units
The distance between the points K and L = \(\sqrt{(x – 9)^{2} + (y – 2)^{2}}\)
6= \(\sqrt{(x – 9)^{2} + (y – 2)^{2}}\)
Squaring on both sides
So,
(x – 9)² + (y – 2)² = 36
The distance between the points J and L = \(\sqrt{(x – 3)^{2} + (y – 2)^{2}}\)
6= \(\sqrt{(x – 3)^{2} + (y – 2)^{2}}\)
Squaring on both sides
So,
(x – 3)² + (y – 2)² = 36
Now,
(x – 9)² + 36 – (x – 3)² = 36
(x – 9)² = (x – 3)²
x² + 81 – 18x = x² + 9 – 6x
18x – 6x = 81 – 9
12x = 72
x = \(\frac{72}{12}\)
x = 6
So,
Substitute the value of x in eq (2)
(6 – 3)² + (y – 2)² = 36
(y – 2)² = 36 – 9
y – 2 = \(\sqrt{27}\)
y = 7.2
Hence, from the above,
We can conclude that the third vertex is: L (6, 7.2)

Topic 7 Fluency Practice

Riddle Rearranging
Solve each equation. Then arrange the answers in order from least to greatest. The letters will spell out the answer to the riddle below.

I can… solve multistep equations.
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 89

Why did the coffee shop server love the job? Because there were so
Envision Math Common Core Grade 8 Answer Key Topic 7 Understand And Apply The Pythagorean Theorem 90
Answer:
The Ascending order of the solutions of the equations is:
M < N < Y < P < A < E < R < K < S

enVision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity

Go through the enVision Math Common Core Grade 8 Answer Key Topic 6 Congruence and Similarity and finish your homework or assignments.

enVision Math Common Core 8th Grade Answers Key Topic 6 Congruence And Similarity

Topic Essential Question
How can you show that two figures are either congruent or similar to one another?
Answer:
When two line segments have the same length, we can say that they are congruent. When two figures have the same shape and size, we can say that the two figures are congruent. These two triangles are congruent. We can also say that their side lengths are the same and that their angle measures are the same

3-ACT MATH

Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 1

Tricks of the Trade
All kinds of objects in nature have symmetry: beehives, pine cones, butterflies, and snowflakes, to name a few. If you look closely, you will start to see patterns left and right. Think about this during the 3-Act Mathematical Modeling lesson.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 2

Topic 6 ënVision STEM Project

Did You Know?
Trees provide wood for cooking and heating for half of the world’s population.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 3
As trees grow, carbon dioxide is removed from the atmosphere for photosynthesis. Forests are called “carbon sinks” because one acre of forest absorbs six tons of carbon dioxide and puts out four tons of oxygen.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 4
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 5

Trees provide lumber for buildings, tools, and furniture. Other products include rubber, sponges, cork, paper, chocolate, nuts, and fruit.
About 30% of the land is covered by forests.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 6
Forests are now being managed to preserve wildlife and old-growth forests, protect biodiversity, safeguard watersheds, and develop recreation, as well as extract timber.

Forests also need to be managed to prevent raging wildfires, invasive species, overgrazing, and disease.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 7

Your Task: Forest Health
The proper management of forests is a growing science. You and your classmates will learn about forest health indicators and use what you know about similar triangles and ratios to gather and interpret data in order to assess the health of a forest.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 8

Topic 6 GET READY!

Review What You Know!

Vocabulary
Choose the best term from the box to complete each definition.
adjacent angles
complementary angles
supplementary angles
vertical angles

Question 1.
_________ have a sum of 90°.
Answer:
We know that,
The “Complementary angles” have a sum of 90°
Hence, from the above,
We can conclude that the best term to complete the given definition is: Complementary angles

Question 2.
_________ share the same ray.
Answer:
We know that,
The “Adjacent Angles” share the same ray
Hence, from the above,
We can conclude that the best term to complete the given definition is: Adjacent angles

Question 3.
_________ are pairs of opposite angles made by intersecting lines.
Answer:
We know that,
The “Vertical Angles” are pairs of opposite angles made by intersecting lines
Hence, from the above,
We can conclude that the best term to complete the given definition is: Vertical angles

Question 4.
__________ have a sum of 180°
Answer:
We know that,
The “Supplementary Angles” have a sum of 180°
Hence, from the above,
We can conclude that the best term to complete the given definition is: Supplementary angles

Multiplying Real Numbers

Simplify the expression.
Question 5.
5 × 2 = ________
Answer:
The given expression is:
5 × 2
Hence, from the above,
We can conclude that
5 × 2 = 10

Question 6.
6 × \(\frac{1}{2}\) = ________
Answer:
The given expression is:
6 × \(\frac{1}{2}\)
So,
6 × \(\frac{1}{2}\)
= \(\frac{6}{2}\)
= 3
Hence, from the above,
We can conclude that
6 × \(\frac{1}{2}\) = 3

Question 7.
12 × \(\frac{1}{3}\) = ________
Answer:
The given expression is:
12 × \(\frac{1}{3}\)
So,
12 × \(\frac{1}{3}\)
= \(\frac{12}{3}\)
= 4
Hence, from the above,
We can conclude that
12 × \(\frac{1}{3}\) = 4

Identifying Points on a Coordinate Plane

Name the location of the point.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 9
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 9
From the given coordinate plane,
We can observe that

Question 8.
point W
Answer:
From the given coordinate plane,
We can observe that point W lies where both the x-axis and y-axis are negative
Hence, from the above,
We can conclude that point W lies in the third quadrant

Question 9.
point X
Answer:
From the given coordinate plane,
We can observe that point X lies where the x-axis is negative and the y-axis is positive
Hence, from the above,
We can conclude that point X lies in the second quadrant

Question 10.
point Y
Answer:
From the given coordinate plane,
We can observe that point Y lies where both the x-axis and y-axis are positive
Hence, from the above,
We can conclude that point Y lies in the first quadrant

Question 11.
point Z
Answer:
From the given coordinate plane,
We can observe that point Z lies where the x-axis is positive and the y-axis is negative
Hence, from the above,
We can conclude that point Z lies in the fourth quadrant

Supplementary Angles

The angles are supplementary. Find the missing angle measure.
Question 12.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 10
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 10
We know that,
The sum of the supplementary angles is: 180°
Now,
Let the missing angle measure be: x°
So,
x° + 130° = 180°
x° = 180° – 130°
x° = 50°
Hence, from the above,
We can conclude that the missing angle measure is: 50°

Question 13.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 11
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 11
We know that,
The sum of the supplementary angles is: 180°
Now,
Let the missing angle measure be: x°
So,
x° + 139° = 180°
x° = 180° – 139°
x° = 41°
Hence, from the above,
We can conclude that the missing angle measure is: 41°

Language Development
Complete the graphic organizer with an illustration for each transformation. Write either congruent or similar to make the given statement true.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 12
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 13
Answer:

Topic 6 PICK A PROJECT

PROJECT 6A
How might an artist use mathematics?
PROJECT: WRITE A BIOGRAPHY
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 14

PROJECT 6B
What geometric shapes do you see around you?
PROJECT: RECORD A VIDEO ABOUT SIMILAR FIGURES
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 15

PROJECT 6C
What different types of bridges have you crossed?
PROJECT: BUILD A MODEL OF A TRUSS BRIDGE
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 16

PROJECT 6D
What shapes tessellate?
PROJECT: DESIGN A TESSELLATION
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 17

Lesson 6.1 Analyze Translations

Solve & Discuss It!
Ashanti draws a trapezoid on the coordinate plane and labels it in Figure 1. Then she draws Figure 2. How can she determine whether the figures have the same side lengths and the same angle measures?
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 18
I can… translate two-dimensional figures.
Answer:
It is given that
Ashanti draws a trapezoid on the coordinate plane and labels it in Figure 1. Then she draws Figure 2.
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 18
From the figure,
We can observe that the first figure was translated or moved to the right by some units and became a second figure
We know that,
A “Translation” is a transformation that moves every point in a figure the same distance in the same direction
We know that,
The pre-image and image in the “Translation” are similar
We know that,
Two figures are said to be similar if they are the same shape. In more mathematical language, two figures are similar if their corresponding angles are congruent, and the ratios of the lengths of their corresponding sides are equal.
Hence, from the above,
We can conclude that by using the “Translation” property, she can determine whether the figures have the same side lengths and the same angle measures

Focus on math practices
Be Precise How do you know that the method you described shows whether the side lengths and angle measures are equal? Explain.
Answer:
We know that,
A “Translation” is a transformation that moves every point in a figure the same distance in the same direction
We know that,
The pre-image and image in the “Translation” are similar
We know that,
Two figures are said to be similar if they are the same shape. In more mathematical language, two figures are similar if their corresponding angles are congruent, and the ratios of the lengths of their corresponding sides are equal.

Essential Question
How does a translation affect the properties of a two-dimensional figure?
Answer:
When you translate something in geometry, you’re simply moving it around. You don’t distort it in any way. If you translate a segment, it remains a segment, and its length doesn’t change. Similarly, if you translate an angle, the measure of the angle doesn’t change.

Try It!

The clients also want the small table below the window moved 5 feet to the right. Where should the architect place the small table? Draw the new location of the table on the plan.
Answer:
It is given that
The clients also want the small table below the window moved 5 feet to the right
Now,
The original plan is:

From the above plan,
We can observe that the window is at most right
So,
When we move the table,
The new location of the table will be below the window
Hence,
The location of the table on the new plan is:

Convince Me!
An equilateral triangle with side lengths 5 inches is translated 3 units down and 2 units right. Describe the shape and dimensions of the translated figure.
Answer:
It is given that
An equilateral triangle with side lengths 5 inches is translated 3 units down and 2 units right.
We know that,
In an equilateral triangle, all the side lengths are equal
Now,
Let the dimensions of an equilateral triangle be (x1, y1), (x2, y2), and (x3, y3)
So,
The dimensions of the translated figure are: (x1 + 2, y1 – 3), (x2 + 2, y2 – 3), and (x3 + 2, y3 – 3)
Now,
Let us suppose the dimensions of an equilateral to be:
(1, 1), (1, 6), and (5, 3)
So,
The dimensions of the translated equilateral triangle are:
(3, -2), (3, 3), and (7, 0)
We know that,
When you translate something in geometry, you’re simply moving it around. You don’t distort it in any way
So,
The shape of the translated figure remains the same as the original figure
Hence,
The representation and shape of the original and translated equilateral triangles are:

Try It!

Triangle ABC is translated 5 units right and 1 unit down. Graph and label the image A’ B’C’. If m∠A = 30° in ΔABC, then what is m∠A in ΔA’B’C’?
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 19
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 19
From the given figure,
The dimensions of ΔABC are:
A (-2, 3), B (-3, -4), and C (-5, -1)
Now,
Let the dimensions of an equilateral triangle be (x1, y1), (x2, y2), and (x3, y3)
So,
The dimensions of the translated figure are: (x1 + 5, y1 – 1), (x2 + 5, y2 – 1), and (x3 + 5, y3 – 1)
So,
The dimensions of the translated triangle (A’B’C’) are:
A (3, 2), B (2, -5), and C (0, -2)
We know that,
A translated figure has the same shape as the original shape i.e, the lengths and the angles of the translated figure are also the same as the original figure
So,
m∠A in Triangle ABC = m∠A in Triangle A’B’C’ = 30°
Hence,
The representation of the original and translated triangles are:

KEY CONCEPT

A translation, or slide, is a transformation that moves Preimage to every point of a figure the same distance and the same direction.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 20

Do You Understand?
Question 1.
Essential Question How does a translation affect the properties of a two-dimensional figure?
Answer:
When you translate something in geometry, you’re simply moving it around. You don’t distort it in any way. If you translate a segment, it remains a segment, and its length doesn’t change. Similarly, if you translate an angle, the measure of the angle doesn’t change.

Question 2.
Construct Arguments Triangle L’M’N’ is the image of triangle LMN after a translation. How are the side lengths and angle measures of the triangles related? Explain.
Answer:
We know that,
When you translate something in geometry, you’re simply moving it around. You don’t distort it in any way. If you translate a segment, it remains a segment, and its length doesn’t change. Similarly, if you translate an angle, the measure of the angle doesn’t change.
Hence, from the above,
We can conclude that
The side lengths and the angle measures of Triangle L’M’N’ is the same as The side lengths and the angle measures of Triangle LMN

Question 3.
Generalize Sanjay determined that one vertex of a figure was mapped to its image by translating the point 2 units left and 7 units down. What is the rule that maps the other vertices of the figure to their images?
Answer:
It is given that
Sanjay determined that one vertex of a figure was mapped to its image by translating the point 2 units left and 7 units down
Now,
Now,
Let the dimensions of any vertex of the given be (x, y)
So,
The dimensions of any vertex of the translated figure are: (x – 2, y + 7)
Hence, from the above,
We can conclude that
The rule that maps the other vertices of the figure to their images is: (x – 2, y – 7)

Do You Know How?
In 4-6, use the coordinate plane.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 21

Question 4.
Which figure is a translation of Figure A? Explain
Answer:
We know that,
When you translate something in geometry, you’re simply moving it around. You don’t distort it in any way. If you translate a segment, it remains a segment, and its length doesn’t change. Similarly, if you translate an angle, the measure of the angle doesn’t change.
So,
When we observe the coordinate plane,
We can see that A and C have the same shape i.e., have the same length and the same angle
Hence, from the above,
We can conclude that
Figure C is a translation of Figure A

Question 5.
Graph the translation of Figure A 3 units right and 4 units up.
Answer:
From the given coordinate plane,
The dimensions of Figure A are:
(-2, -1), (-4, -1), (-4, -2), (-3, -2), (-3, -3), (-4, -3), (-4, -4), and (-2, -4)
So,
The rule that maps the vertices of the given figure to their images is: (x + 3, y + 4)
So,
The vertices of the image are:
(1, 3), (-1, 3), (-1, 2), (0, 2), (0, 1), (-1, 1), (-1, 0), and (1, 0)
Hence,
The representation of Figure A and its translated figure is:

Question 6.
Describe the translation needed to move Figure B to the same position as the image from Item 5.
Answer:
From the given coordinate plane,
The dimensions of figure B are:
(-2, 4), (-4, 4), (-4, 3), (-3, 3), (-3, 2), (-4, 2), (-4, 1), and (-2, 1)
Hence,
The translation needed to move figure B to the same position as the image from Item 5 is:
The X-axis: Translate 3 units right
The Y-axis: Translate 1 unit down

Practice & Problem Solving

Question 7.
Graph G’R’A’M’, the image of GRAM after a translation 11 units right and 2 units up.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 22
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 22
From the given coordinate plane,
The dimensions of GRAM are:
G (-8, 2), R (-8, 6), A (-4, 6), and M (-5, 2)
So,
After a translation of 11 units right and 2 units up,
The dimensions of G’R’A’M’ are:
G’ (-8 + 11, 2 + 2), R’ (-8 + 11, 6 + 2), A’ (-4 + 11, 6 + 2), and M’ (-5 + 11, 2 + 2)
So,
G’ (3, 4), R’ (3, 8), A’ (7, 8), and M’ (6, 4)
Hence,
The representation of GRAM and its image G’R’A’M’ is:

Question 8.
∆A’ B’ C’ is a translation of ∆ABC. Describe the translation.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 23
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 23
From the coordinate plane,
The dimensions of ΔABC are:
A (1, -5), B (-2, -2), and C (0, 0)
Now,
The dimensions of ΔA’B’C’ are:
A’ (0, -1), B’ (-3, 2), and C’ (-1, 4)
So,
By observing the dimensions of ΔABC and ΔA’B’C’,
The translation between ΔABC and ΔA’B’C is:
The x-axis: Translate 1 unit left
The y-axis: Translate 4 units up

Question 9.
Which triangle is the image of ∆DEF after a translation? Describe the translation.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 24
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 24
We know that,
When you translate something in geometry, you’re simply moving it around. You don’t distort it in any way. If you translate a segment, it remains a segment, and its length doesn’t change. Similarly, if you translate an angle, the measure of the angle doesn’t change.
So,
From the given figure,
We can observe that
ΔMNO has the same shape as ΔDEF
So,
The image of ΔDEF is: ΔMNO
Now,
The dimensions of ΔDEF are:
D (-8, -10), F (-6, -10), and E (-8, -4)
Now,
The dimensions of ΔMNO are:
M (2, -10), O (4, -10), and N (2, -4)
So,
By observing the dimensions of ΔDEF and ΔMNo,
The translation between ΔDEF and ΔMNO is:
The x-axis: Translate 10 units right
The y-axis: No Translation required

Question 10.
The vertices of figure QRST are translated 3 units left and 11 units down to form figure Q’R’S’T’. Explain the similarities and differences between the two figures.
Answer:
It is given that
The vertices of figure QRST are translated 3 units left and 11 units down to form figure Q’R’S’T’.
Hence,
The similarities between figure QRST and figure Q’R’S’T’ are:
a. The two figures have the same side length
b. The two figures have the same angle measure
c. The two figures have the same shape
The differences between figure QRST and figure Q’R’S’T’ are:
a. Different dimensions of the vertices of QRST and Q’R’S’T’
b. Different positions of figure QRST and figure Q’R’S’T’

Question 11.
Graph the image of the given triangle after a translation of 3 units right and 2 units up.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 25
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 25
From the given coordinate plane,
The dimensions of the given triangle are:
(-3, 4), (-5, -1), and (-8, 3)
Now,
After a translation 3 units right and 2 units up,
The dimensions of the given triangle are:
(-3 + 3, 4 + 2), (-5 + 3, -1 + 2), and (-8 + 3, 3 + 2)
(0, 6), (-2, 1), and (-5, 5)
Hence,
The representation of the given triangle and its image is:

Question 12.
Quadrilateral P’Q’R’ S’ is the image of quadrilateral PQRS after a translation.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 26
Answer:
It is given that
Quadrilateral P’Q’R’ S’ is the image of quadrilateral PQRS after a translation.
We know that,
When you translate something in geometry, you’re simply moving it around. You don’t distort it in any way. If you translate a segment, it remains a segment, and its length doesn’t change. Similarly, if you translate an angle, the measure of the angle doesn’t change.

a. If the length of side PQ is about 2.8 units, what is the length of side P’ Q’?
Answer:
It is given that
The length of the side PQ is about 2.8 units
Hence, from the above,
We can conclude that the length of side P’Q’ is also about 2.8 units

b. If m∠R = 75°, what is m∠R’?
Answer:
It is given that
m∠R = 75°
Hence, from the above,
We can conclude that
m∠R’ = 75°

Question 13.
Higher-Order Thinking A farmer has a plot of land shaped like the figure in the graph. There is another identical plot of land 120 yards east and 100 yards north of the original plot.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 27
a. Draw the image after the given translation.
Answer:
It is given that
A farmer has a plot of land shaped like the figure in the graph. There is another identical plot of land 120 yards east and 100 yards north of the original plot.
Now,
The given plot of land is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 27
Now,
From the given plot of land,
The dimensions of land are:
(0, 0), (0, 300), (300, 0), and (300, 300)
Now,
After the translation of 120 units right and 100 units up,
The dimensions of the identical plot are:
(0 + 120, 0 + 100), (0 + 120, 300 + 100), (300 + 120, 0 + 100), and (300 + 120, 300 + 100)
(120, 100), (120, 400), (420, 100), and (420, 400)
Hence,
The representation of the plot and its image after the translation is:

b. Find the combined area of the 2 plots in square yards.
Answer:
From part (a),
We can observe that the shape of the plot of land and its identical is like a square
We know that,
The square has the equal side lengths
Now,
From part (a),
We can observe that the side length of the plot of land and its identical is: 300 yards
Now,
We know that,
The area of square = Side²
So,
The area of the plot of land = 300²
= 90,000 yard²
The area of the identical plot of land = 300²
= 90,000 yard²
So,
The combined area of the 2 plots = 90,000 + 90,000
= 1,80,000 yard²
Hence, from the above,
We can conclude that the combined area of the 2 plots is: 1,80,000 yard²

Assessment Practice
Question 14.
What is true about the preimage of a figure and its image created by a translation? Select all that apply.
☐ Each point in the image moves the same distance and direction from the preimage.
☐ Each point in the image has the same x-coordinate as the corresponding point in the preimage.
☐ Each point in the image has the same y-coordinate as the corresponding point in the preimage.
☐ The preimage and the image are the same size.
☐ The preimage and the image are the same shape.
Answer:
We know that,
When you translate something in geometry, you’re simply moving it around. You don’t distort it in any way. If you translate a segment, it remains a segment, and its length doesn’t change. Similarly, if you translate an angle, the measure of the angle doesn’t change.
Hence,
The statements that are true about the preimage of a figure and its image created by a translation are:

Question 15.
The vertices of parallelogram QUAD are Q(-7, -7), U(-6, -4), A(-2,-4), and D(-3, -7).
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 28
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 28
Now,
From the given coordinate plane,
The dimensions of the parallelogram QUAD are:
Q (-7, -7), U (-6, -4), A (-2, -4), and D (-3, -7)
Now,
After the translation of 11 units right and 9 units up,
The dimensions of the parallelogram QUAD are:
Q’ (-7 + 11, -7 + 9), U’ (-6 + 11, -4 + 9), A’ (-2 + 11, -4 + 9), and D’ (-3 + 11, -7 + 9)
Q’ (4, 2), U’ (5, 5), A’ (9, 5), and D’ (8, 2)

PART A
Graph and label the image of QUAD after a translation 11 units right and 9 units up.
Answer:
The representation of the parallelogram QUAd and its image is:

PART B
If m∠U = 110°, what is m∠ U’?
Answer:
We know that,
When you translate something in geometry, you’re simply moving it around. You don’t distort it in any way. If you translate a segment, it remains a segment, and its length doesn’t change. Similarly, if you translate an angle, the measure of the angle doesn’t change.
Hence, from the above,
We can conclude that
m∠U’ = 110°

PART C
If the length of side UA is 4 units, what is the length of side U’ A’?
Answer:
We know that,
When you translate something in geometry, you’re simply moving it around. You don’t distort it in any way. If you translate a segment, it remains a segment, and its length doesn’t change. Similarly, if you translate an angle, the measure of the angle doesn’t change.
Hence, from the above,
We can conclude that
The length of the side U’ A’ is: 4 units

Lesson 6.2 Analyze Reflections

Solve & Discuss It!
Dale draws a triangle on grid paper and labels it in Figure 1. Then using his pencil as a guide, he draws another triangle directly on the opposite side of the pencil so that the vertical side is now one square to the right of the pencil instead of one square to the left of the pencil. He labels this triangle in Figure 2. How are the figures the same? How are they different?
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 29
I can… reflect two-dimensional figures.
Answer:
Dale draws a triangle on grid paper and labels it in Figure 1. Then using his pencil as a guide, he draws another triangle directly on the opposite side of the pencil so that the vertical side is now one square to the right of the pencil instead of one square to the left of the pencil. He labels this triangle in Figure 2.
Hence,
The representation of Figure 1 and Figure 2 is:

So,
From the above representation,
The similarities between Figure 1 and Figure 2 are:
a. Both the figures have the same side lengths
b. Both the figures have the same angle measures
c. Both the figures have the same size
d. Both the figures have the same distance
The differences between Figure 1 and Figure 2 are:
a. The positions of both figures are different
b. The orientations of both figures are different
c. The directions of both the figures are different

Look for Relationships
What do you notice about the size, shape, and direction of the two figures?
Answer:
The similarities between Figure 1 and Figure 2 are:
a. Both the figures have the same side lengths
b. Both the figures have the same angle measures
c. Both the figures have the same size
d. Both the figures have the same distance
The differences between Figure 1 and Figure 2 are:
a. The positions of both figures are different
b. The orientations of both figures are different
c. The directions of both the figures are different

Focus on math practices
Reasoning Dale draws a line in place of his pencil and folds the grid paper along the line. How do the triangles align when the grid paper is folded? Explain.
Answer:
It is given that
Dale draws a line in place of his pencil and folds the grid paper along the line
Now,
The representation of Figure 1 and Figure 2 are:

Now,
From the given figure,
We can observe that the two triangles will stack on each other when the grid paper is folded i.e.,
a. The vertical side of figure 2 is on top of the vertical side of figure 1
b. The base of figure 2 is on top of the base of figure 1
c. The hypotenuse of figure 2 is on top of the hypotenuse of figure 1

Essential Question
How does a reflection affect the properties of a two-dimensional figure?
Answer:
When the reflection takes place along the x-axis,
The values of x will remain constant and the values of y will have a sign change
Ex:
When (x, y) and (-x, y) reflects along the x-axis,
The reflection of (x, y) will become (x, -y)
The reflection of (-x, y) will become (-x, -y)
When the reflection takes place along the y-axis,
The values of y will remain constant and the values of x will have a sign change
Ex:
When (x, y) and (x, -y) reflects along the y-axis,
The reflection of (x, y) will become (-x, y)
The reflection of (x, -y) will become (-x, -y)

Try It!

While updating the design, the architect accidentally clicked on the chair and reflected it across the centerline. Draw the new location of the chair on the plan.

Answer:
It is given that
While updating the design, the architect accidentally clicked on the chair and reflected it across the centerline.
Hence,
The representation of the new location of the chair is:

Convince Me!
How do the preimage and image compare after a reflection?
Answer:
A reflection is a transformation that turns a figure into its mirror image by flipping it over a line. The line of reflection is the line that a figure is reflected over. If a point is on the line of reflection then the image is the same as the preimage. Otherwise,
the image is not the same as the preimage. Images are always congruent to preimages

Try It!

Quadrilateral KLMN has vertices at K(2, 6), L(3, 8), M(5, 4), and N(3, 2). It is reflected across the y-axis, resulting in quadrilateral K’L’M’N’. What are the coordinates of point N’?
Answer:
It is given that
Quadrilateral KLMN has vertices at K(2, 6), L(3, 8), M(5, 4), and N(3, 2). It is reflected across the y-axis, resulting in quadrilateral K’L’M’N’
Now,
We know that,
When (x, y) and (x, -y) reflects along the y-axis,
The reflection of (x, y) will become (-x, y)
The reflection of (x, -y) will become (-x, -y)
So,
The reflection of N (3, 2) i.e., the coordinates of N’ is: (-3, 2)
Hence, from the above,
We can conclude that the coordinates of N’ are: (-3, 2)

Try It!

Polygon ABCDE is reflected across the line x = -2. Graph and label the image A’B’C’D’E’. Is m∠A= M∠A? Explain.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 30
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 30
Now,
From the given coordinate plane,
The vertices of polygon ABCDE are:
A (-4, 4), B (-3, 3), C (-3, 2), D (-5, 1), and E (-5, 3)
It is given that polygon ABCDE is reflected along x = -2 i.e., alone the x-axis
We know that,
When (x, y) and (-x, y) reflects along the y-axis,
The reflection of (x, y) will become (x, -y)
The reflection of (-x, y) will become (-x, -y)
So,
The vertices of the reflection of polygon ABCDE i..e, A’B’C’D’E’ are:
A’ (-4, -4), B’ (-3, -3), C’ (-3, -2), D’ (-5, -1), and E’ (-5, -3)
We know that,
In reflection,
The side lengths and the angle measures in the image and the preimage are the same
Hence,
The representation of polygon ABCDE and its reflection polygon A’B’C’D’E’ is:

Hence,
m ∠A = M ∠A

KEY CONCEPT

A reflection, or flip, is a transformation that flips a figure across a line of reflection. The preimage and image are the same distance from the line of reflection but on opposite sides. They have the same size and shape but different orientations.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 31

Do You Understand?
Question 1.
Essential Question How does a reflection affect the properties of a two-dimensional figure?
Answer:
When the reflection takes place along the x-axis,
The values of x will remain constant and the values of y will have a sign change
Ex:
When (x, y) and (-x, y) reflects along the x-axis,
The reflection of (x, y) will become (x, -y)
The reflection of (-x, y) will become (-x, -y)
When the reflection takes place along the y-axis,
The values of y will remain constant and the values of x will have a sign change
Ex:
When (x, y) and (x, -y) reflects along the y-axis,
The reflection of (x, y) will become (-x, y)
The reflection of (x, -y) will become (-x, -y)

Question 2.
Generalize What do you notice about the corresponding coordinates of the preimage and image after a reflection across the x-axis?
Answer:
When the reflection takes place along the x-axis,
The values of x will remain constant and the values of y will have a sign change
Ex:
When (x, y) and (-x, y) reflects along the x-axis,
The reflection of (x, y) will become (x, -y)
The reflection of (-x, y) will become (-x, -y)

Question 3.
Construct Arguments Jorge said the y-values would stay the same when you reflect a preimage across the line y = 5 since the y-values stay the same when you reflect a preimage across the y-axis. Is Jorge correct? Explain.
Answer:
It is given that
Jorge said the y-values would stay the same when you reflect a preimage across the line y = 5 since the y-values stay the same when you reflect a preimage across the y-axis.
Now,
We know that,
When the reflection takes place along the y-axis,
The values of y will remain constant and the values of x will have a sign change
Ex:
When (x, y) and (x, -y) reflects along the y-axis,
The reflection of (x, y) will become (-x, y)
The reflection of (x, -y) will become (-x, -y)
Hence, from the above,
We can conclude that Jorge is correct

Do You Know How?
Question 4.
Is AX’ Y’ Z’ a reflection of AXYZ across line g?
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 32
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 32
Now,
From the given figure,
We can observe that ΔXYZ is reflected across the line g i.e., y-axis
We know that,
When the reflection takes place along the y-axis,
The values of y will remain constant and the values of x will have a sign change
Ex:
When (x, y) and (x, -y) reflects along the y-axis,
The reflection of (x, y) will become (-x, y)
The reflection of (x, -y) will become (-x, -y)
So,
From the figure,
We can observe that
The negative x-coordinates of the vertices of ΔXYZ became the positive x -coordinates for Δ X’Y’Z’
Hence, from the above,
We can conclude that ΔX’Y’Z’ is the reflection of ΔXYZ across the line g

Use the coordinate grid below for 5 and 6.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 33

Question 5.
Describe the reflection of figure EFGH.
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 33
From the given coordinate plane,
We can observe that
The reflection of figure EFGH is: Figure E’F’G’H’
Now,
We can observe that
The reflection of the figure EFGH takes place across the x-axis
So,
The x-coordinates of the vertices of the reflection of the figure EFGH will be constant and only y-coordinates will have a change in value
Hence,
The figure EFGH will flip i.e., top becomes down and vice-versa to form a reflection i.e., figure E’F’G’H’

Question 6.
Draw the image that would result from a reflection of figure E’F’G’H across the line x = -1.
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 33
Now,
From the reflection of EFGH i.e., figure E’F’G’H’,
We can observe that the vertices of the figure E’F’G’H’ are:
E’ (-8, 7), F’ (-5, 5), G’ (-4, 6), and H’ (-2, 6)
Now,
To form the image of the figure E’F’G’H’,
We need to reflect the figure E’F’G’H’ across the y-axis
When the reflection takes place along the x-axis,
The values of x will remain constant and the values of y will have a sign change
Ex:
When (x, y) and (-x, y) reflects along the x-axis,
The reflection of (x, y) will become (x, -y)
The reflection of (-x, y) will become (-x, -y)
So,
The vertices for the image of the figure E’F’G’H’ are:
E’ (-8, -7), F’ (-5, -5), G’ (-4, -6), and H’ (-2, -6)
Hence,
The representation of the figure E’F’G’H’ and its image is:

Practice & Problem Solving

Question 7.
Leveled Practice Trapezoid ABCD is shown. Draw the reflection of trapezoid ABCD across the y-axis.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 34
Plot the points and draw trapezoid A’ B’C’D’.
Answer:
From the given trapezoid ABCD,
The vertices are:
A (2, 8), B (6, 8), C (8, 3), and D (1, 3)
It is given that
Draw the reflection of trapezoid ABCD across the y-axis i.e., y is constant
Now,
We know that,
When the reflection takes place along the y-axis,
The values of y will remain constant and the values of x will have a sign change
Ex:
When (x, y) and (x, -y) reflects along the y-axis,
The reflection of (x, y) will become (-x, y)
The reflection of (x, -y) will become (-x, -y)
So,
The vertices for the reflection of trapezoid ABCD are:
A’ (-2, 8), B (-6, 8), C’ (-8, 3), and D (-1, 3)
So,
The points of the preimage and image are:

Hence,
The representation of trapezoid A’B’C’D’ is:

Question 8.
Reasoning is triangle A’ B’C’a reflection of triangle ABC across the line? Explain.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 35
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 35
Now,
From the given figure,
We can observe that the reflection of ΔABC takes place across the y-axis
Now,
When the reflection takes place along the y-axis,
The values of y will remain constant and the values of x will have a sign change
Ex:
When (x, y) and (x, -y) reflects along the y-axis,
The reflection of (x, y) will become (-x, y)
The reflection of (x, -y) will become (-x, -y)
So,
From the vertices of ΔABC,
The x-coordinates are negative and the y-coordinates are positive
So,
For the reflection of ΔABC along the y-axis,
The x-coordinates will have to become positive and the y-coordinates will be positive as in the vertices of ΔABC
Hence, from the above,
We can conclude that ΔA’B’C’ is the reflection of ΔABC across the given line

Question 9.
Your friend gives you the graph of quadrilateral ABCD and its image, quadrilateral A’B’C’D’. What reflection produces this image?
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 36
Answer:
It is given that
Your friend gives you the graph of quadrilateral ABCD and its image, quadrilateral A’B’C’D’
Now,
The quadrilateral ABCD and its image quadrilateral A’B’C’D’ is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 36
Now,
From the given figure,
We can observe that
The quadrilateral ABCD and its image will have the same y-coordinates but the x-coordinates are different
We know that,
When the reflection takes place across the y-axis,
The y-coordinates are the same for the image and the preimage
The x-coordiantes have sign changes with the same values for the image and the preimage
Hence, from the above,
We can conclude that the reflection across the y-axis produces the image quadrilateral A’B’C’D’

Question 10.
Construct Arguments Your friend incorrectly says that the reflection of ∆EFG to its image ∆E’ F’G’ is a reflection across the y-axis.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 37
a. What is your friend’s mistake?
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 37
From the above figure,
We can observe that
For the vertices of the given figure,
The x-coordinates remain the same whereas the y-coordinates are different
We know that,
When the reflection takes place across the x-axis,
The x-coordinates of the preimage and the image are the same
The y-coordinates of the preimage and the image will have sign change with the same values
Hence, from the above,
We can conclude that the reflection of ΔEFG takes pace across the x-axis instead of across the y-axis

b. What is the correct description of the reflection?
Answer:
From the given figure,
We can observe that
For the vertices of the given figure,
The x-coordinates remain the same whereas the y-coordinates are different
We know that,
When the reflection takes place across the x-axis,
The x-coordinates of the preimage and the image are the same
The y-coordinates of the preimage and the image will have sign change with the same values
Hence, from the above,
We can conclude that the reflection of ΔEFG to its image ΔE’F’G’ takes pace across the x-axis

Question 11.
Make Sense and Persevere The vertices of ∆ABC are A(-5, 5), B(-2,5), and C(-2, 3). If ∆ ABC is reflected across the line y = -1, find the coordinates of the vertex C’
Answer:
It is given that
The vertices of ∆ABC are A(-5, 5), B(-2,5), and C(-2, 3) and ∆ ABC is reflected across the line y = -1
We know that,
When the reflection takes place across the y-axis,
The y-coordinates of the preimage and the image are the same
The x-coordinates of the preimage and the image will have sign change with the same values
So,
The reflection of the vertex C (-2, 3) is: (2, 3)
Hence, from the above,
We can conclude that the coordinates of the vertex C’ i.e., the reflection of the vertex C is: (2, 3)

Question 12.
Higher Order Thinking What reflection of the parallelogram ABCD results in image A’B’C’D?
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 38
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 38
From the given figure,
We can observe that the parallelogram ABCD and its reflection A’B’C’D’ are parallel to the x-axis
Now,
We can observe that,
For both the parallelogram ABCD and its reflection A’B’C’D’,
The x-coordinates are changing but the y-coordinates remain the same
Now,
We know that,
When the reflection takes place across the y-axis,
The y-coordinates of the preimage and the image are the same
The x-coordinates of the preimage and the image will have sign change with the same values
Hence, from the above,
We can conclude that the reflection across the y-axis of the parallelogram ABCD results in image A’B’C’D

Assessment Practice
Question 13.
∆JAR has vertices J(4, 5), A6, 4), and R(5,2). What graph shows ∆JAR and its image after a reflection across the line y = 1?
PART A
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 39
Answer:
It is given that
∆JAR has vertices J(4, 5), A6, 4), and R(5,2)
Now,
We know that,
The reflection across the y-axis is:
The y -coordinates are the same
The x-coordinates will have sign changes with the same value
So,
The reflection of the vertices of ΔJAR is:
J’ (-4, 5), A’ (-6, 4), and R (-5, 2)
Hence,f rom the above,
We can conclude that option D matches with the given vertices of the reflection i.e., ΔJ’A’R’

PART B
The measure of ∠A = 90°. What is m∠A’?
Answer:
We know that,
In Reflection,
The side lengths and the angle measures of the preimage and the image are the same
Hence, from the above,
We can conclude that
∠A = ∠A’ = 90°

Lesson 6.3 Analyze Rotations

Explain It!
Maria boards a car at the bottom of the Ferris wheel. She rides to the top, where the car stops. Maria tells her friend that she completed \(\frac{1}{4}\) of the turn before the car stopped.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 40
I can… rotate a two-dimensional figure.

A. Do you agree with Maria? Explain.
Answer:
It is given that
Maria boards a car at the bottom of the Ferris wheel. She rides to the top, where the car stops. Maria tells her friend that she completed \(\frac{1}{4}\) of the turn before the car stopped.
Now,
We know that,
From the given figure,
The Ferris wheel looks like a circle
We know that
The total angle measure of a circle (Ferris wheel) is: 360°
But,
It is given that
Maria tells her friend that she completed \(\frac{1}{4}\) of the turn before the car stopped
But, from the figure,
We can observe that she completed the \(\frac{1}{2}\) of the ride
Hence, from the above,
We can conclude that we can’t agree with Maria

B. How could you use angle measures to describe the change in position of the car?
Answer:
We know that,
From the given figure,
The Ferris wheel looks like a circle
We know that
The total angle measure of a circle (Ferris wheel) is: 360°
So,
The starting position of the car in terms of angle measure is given as 0°
The \(\frac{1}{2}\) of the position of the car in terms of angle measure = \(\frac{360°}{2}\)
= 180°
Hence, from the above,
We can conclude that
In terms of angle measures,
The starting position of the car is: 0°
The \(\frac{1}{2}\) of the car is: 180°

Focus on math practices
Construct Arguments How can you describe Maria’s change in position when her car returns to the position at which she began the ride?
Answer:
We know that,
The starting position of the car is: 0°
The \(\frac{1}{2}\) of the car is: 180°
Now,
If Maria’s car returns to the position at which she began the ride, then
Maria has completed the Ferris wheel (or) Maria returned back from her previous \(\frac{1}{2}\) of the position of the car
Hence,
In terms of angle measures,
The change in Maria’s position when her car returns to the position at which she began the ride is: 360° (or) -180°
Here,
-180° represents that Maria returned back from her previous \(\frac{1}{2}\) of the position of the car

Essential Question
How does rotation affect the properties of a two-dimensional figure?
Answer:
When you rotate a two-dimensional figure, you are just moving it.
Ex:
If you rotate a rectangle, then it will remain a rectangle, just moved wherever you move it. This is similarly the same with an angle and aside length, the measure of the angle and the side length won’t change.

Try It!

The architect continues to rotate the umbrella in a counterclockwise direction until it is in its original position. What is the angle of this rotation?

Answer:
It is given that
The architect continues to rotate the umbrella in a counterclockwise direction until it is in its original position.
Now,
We know that,
If any figure rotates until it comes to its original position again, then that means the figure completed a full cycle (or) revolution and the angle of the full cycle is: 360°
Hence, from the above,
We can conclude that the architect continues to rotate the umbrella for 360° in a counterclockwise direction until it is in its original position

Convince Me!
How does an image compare to its preimage after a -45° rotation?
Answer:

Try It!

The coordinates of the vertices of quadrilateral HIJK are H(1,4), I(3, 2), J(-1,-4), and K(-3, -2). If quadrilateral HIJK is rotated 270° about the origin, what are the vertices of the resulting image, quadrilateral H’I’I’K?
Answer:
It is given that
The coordinates of the vertices of quadrilateral HIJK are H(1,4), I(3, 2), J(-1,-4), and K(-3, -2)
Now,.
We know that,
The change in the x and y-coordinates for the given angle of rotation is:

Now,
It is given that to rotate the quadrilateral HIJK 270° about the origin to form the quadrilateral H’I’J’K’
So,
The vertices of the quadrilateral H’I’J’K’ are:
H’ (4, -1), I’ (2, -3), J’ (-4, 1), K’ (-2, 3)
Hence,
The representation of the quadrilateral HIJK and its image H’I’J’K’ is:

Try It!

Describe the rotation that maps ∆FGH to ∆FG’H’.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 41
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 41
Now,
From the given coordinate plane,
The vertices of ΔFGH are:
F (-5, -2), G (-1, -2), and H (-1, 1)
The vertices of ΔF’G’H’ are:
F’ (5, 2), G’ (1, 2), and H’ (1, -1)
Now,
To find the rotation that maps ΔFGH through ΔF’G’H’, the following steps are:
Step 1:
Draw rays from the origin through point G and point G’
Step 2:
Measure the angle formed by the rays
So,
The representation of ΔFGH and its image ΔF’G’H’ with its angle of rotation is:

Hence, from the above,
We can conclude that the angle of rotation that maps ΔFGH through ΔF’G’H’ is: 180°

KEY CONCEPT

A rotation is a transformation that turns a figure about a fixed point called the center of rotation. The angle of rotation is the number of degrees the figure is rotated. The x- and y-coordinates change in predictable ways when rotated.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 42

Do You Understand?
Question 1.
Essential Question How does rotation affect the properties of a two-dimensional figure?
Answer:
When you rotate a two-dimensional figure, you are just moving it.
Ex:
If you rotate a rectangle, then it will remain a rectangle, just moved wherever you move it. This is similarly the same with an angle and aside length, the measure of the angle and the side length won’t change.

Question 2.
Reasoning If a preimage is rotated 360 degrees about the origin how can you describe its image?
Answer:
We know that,
To complete the full cycle i.e., to a preimage to return to its original position, the angle measure is: 360°
Hence, from the above,
We can conclude that
If a preimage is rotated 360° about the origin, then the image and the preimage are the same

Question 3.
Construct Arguments In Example 3, side AB is parallel to side DC. How are side A’ B’ and side D’ C’ related? Explain.

Answer:
In Example 3,
The given two-dimensional figure is a parallelogram
We know that,
In a parallelogram, the opposite sides have the same side lengths
So,
Now,
It is given that
In parallelogram ABCD,
AB is parallel to CD
So,
In parallelogram A’B’C’D’,
A’B’ is parallel to C’D’ since these two sides are just the images of the sides AB and CD
Hence, from the above,
We can conclude that A’B’ is parallel to C’D’

Do You Know How?
Question 4.
The coordinates of the vertices of rectangle ABCD are A(3,-2), B(3, 2), C(-3, 2), and D(-3,-2).
a. Rectangle ABCD is rotated 90° about the origin. What are the coordinates of the vertices of rectangle A’B’C’D’?
Answer:
It is given that
The coordinates of the vertices of rectangle ABCD are A(3,-2), B(3, 2), C(-3, 2), and D(-3,-2).
Now,
We know that,
The change in the x and y-coordinates for the given angle of rotation is:

Now,
It is given that to rotate the rectangle ABCD 90° about the origin to form the rectangle A’B’C’D’
So,
The vertices of the rectangle A’B’C’D’ are:
A’ (2, 3), B’ (-2, 3), C’ (-2, -3), and D’ (2, -3)
Hence,
The representation of the rectangle ABCD and its image rectangle A’B’C’D’ is:

b. What are the measures of the angles of A’B’C’D’?
Answer:
From part (a),
We can observe that all the angles of the rectangle A’B’C’D’ are the same
Hence, from the above,
We can conclude that the angle measures of the rectangle A’B’C’D’ are:
∠A = 90°, ∠B = 90°, ∠C = 90°,and ∠D = 90°

Question 5.
Describe the counterclockwise rotation that maps ∆QRS to ∆Q’R’S.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 43
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 43
Now,
From the given coordinate plane,
The vertices of ΔQRS are:
Q (6, 2), R (4, 9), and S (2, 7)
The vertices of ΔQ’R’S’ are:
Q’ (2, -6), R’ (9, -4), and S’ (7, -2)
Now,
To find the rotation that maps ΔQRS through ΔQ’R’S’, the following steps are:
Step 1:
Draw rays from the origin through point Q and point Q’
Step 2:
Measure the angle formed by the rays
So,
The representation of ΔQRS and its image ΔQ’R’S’ with its angle of rotation is:

Hence, from the above,
We can conclude that the angle of rotation that maps ΔQRS through ΔQ’R’S’ is: 90°

Practice & Problem Solving

Question 6.
What is the angle of rotation about the origin that maps △ΡQR to △Ρ’ Ο’ R’?
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 44
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 44
Now,
From the given coordinate plane,
The vertices of ΔPQR are:
P (3, 3), Q (5, 3), and R (5, 7)
The vertices of ΔP’Q’R’ are:
P’ (-3, 3), Q’ (-3, 5), and S’ (-7, 5)
Now,
To find the rotation that maps ΔPQR through ΔP’Q’R’, the following steps are:
Step 1:
Draw rays from the origin through point P and point P’
Step 2:
Measure the angle formed by the rays
So,
The representation of ΔPQR and its image ΔP’Q’R” with its angle of rotation is:

Hence, from the above,
We can conclude that the angle of rotation that maps ΔPQR through ΔP’Q’R’ is: 90°

Question 7.
Is △X’ Y’Z’ a rotation of △XYZ? Explain.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 45
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 45
From the given coordinate plane,
The vertices of ΔXYZ are:
X (-2, 3), Y (-5, 4), and Z (-2, 7)
The vertices of ΔX’Y’Z’ are:
X’ (3, 2), Y’ (4, 5), and Z’ (7, 2)
Now,
To find the angle of rotation,
Compare the x and y-coordinates of ΔXYZ and ΔX’Y’Z’
So,
(x, y) before rotation ——-> (y, -x) after rotation
We know that,

Hence, from the above,
We can conclude that ΔX’Y’Z’ is a rotation of ΔXYZ

Question 8.
△PQR is rotated 270° about the origin. Graph and label the coordinates of P’, Q’, and R’.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 46
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 46
Now,
From the given coordinate plane,
The vertices of ΔPQR are:
P (2, 3), Q (4, 6), and R (2, 7)
It is given that
Rotate ΔPQR 270° at the origin
We know that,

So,
The vertices of ΔP’Q’R’ when the angle of rotation is 270° are:
P’ (3, -2), Q’ (6, -4), and R’ (7, -2)
Hence,
The representation of ΔPQR and its image ΔP’Q’R’ is:

Question 9.
Is △P’ Q’R’a 270° rotation of △PQR about the origin? Explain.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 47
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 47
From the given coordinate plane,
The vertices of ΔPQR are:
P (3, 3), Q (7, 4), and R (3, 5)
The vertices of ΔP’Q’R’ are:
P’ (-3, 3), Q’ (-4, 7), and R’ (-5, 3)
Now,
To find the angle of rotation,
Compare the x and y-coordinates of ΔPQR and ΔP’Q’R’
So,
(x, y) before rotation ——-> (-y, x) after rotation
We know that,

Hence, from the above,
We can conclude that ΔP’Q’R’ is a rotation of ΔPQR

Question 10.
Reasoning Explain why any rotation can be described by an angle between 0° and 360°.
Answer:
If you rotate an object 360°, it’s like the object never moved because the object would still be in the same spot as if you didn’t move it.
Hence,
Any rotation can be described by an angle of 0° to 360°

Question 11.
Rotate rectangle KLMN 270° about the origin.
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 48
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 48
Now,
From the given coordinate plane,
The vertices of rectangle KLMN are:
K (-3, 2), L (-5, 2), M (-5, 4), and N (-3, 4)
It is given that
Rotate rectangle KLMN 270° at the origin
We know that,

So,
The vertices of rectangle K’L’M’N’ when the angle of rotation is 270° are:
K’ (2, 3), L’ (2, 5), M’ (4, 5), and N’ (4, 3)
Hence,
The representation of rectangle KLMN and its image rectangle K’L’M’N’ is:

 

Question 12.
Higher-Order Thinking An architect is designing a new windmill with four sails. In her sketch, the sails’ center of rotation is the origin, (0, 0), and the tip of one of the sails, point Q, has coordinates (2, -3). She wants to make another sketch that shows the windmill after the sails have rotated 270° about their center of rotation. What would be the coordinates of?
Answer:
It is given that
An architect is designing a new windmill with four sails. In her sketch, the sails’ center of rotation is the origin, (0, 0), and the tip of one of the sails, point Q, has coordinates (2, -3). She wants to make another sketch that shows the windmill after the sails have rotated 270° about their center of rotation
So,
We have to rotate point Q 270° about the origin
We know that,

So,
When we rotate any point 270° about the origin,
(x, y) before rotation ——–> (y, -x)
So,
The representation of point Q after representation is: (-3, -2)
Hence,
The representation of point Q and its image Q’ is:

Assessment Practice
Question 13.
A rotation about the origin maps △TRI to △T’ R’I’.
PART A
Which graph shows an angle you could measure to find the angle of rotation about the origin?
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 49
Answer:
It is given that
A rotation about the origin maps △TRI to △T’ R’I’
Now,
We know that,
We can find the angle of rotation only when the vertex maps with its image but not with any other images
Hence, from the above,
We can conclude that option A matches the given situation

PART B
What is the angle of rotation about the origin?
A. 90°
B. 180°
C. 270°
D. 360°
Answer:
From part (a),
When we observe option A,
The vertices of ΔTRI are:
T (-3, 3), R (-5, 3), and I (-4, 5)
The vertices of ΔT’R’I’ are:
T’ (3, -3), R’ (5, -3), and I’ (4, -5)
We know that,

So,
When we compare the vertices of ΔTRI and ΔT’R’I’,
We can observe that
(x, y) before rotation ———–> (-x, -y) after rotation
Hence, from the above,
We can conclude that the angle of rotation about the origin is: 180°

Lesson 6.4 Compose Transformations

Solve & Discuss It!
How can you map Figure A onto Figure B?
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 50
I can… describe and perform a sequence of transformations.
Answer:
The given figure is:
Envision Math Common Core 8th Grade Answer Key Topic 6 Congruence And Similarity 50
Now,
The steps to obtain Figure B from Figure A are:
Step 1:
Reflect Figure A across the x-axis
Step 2:
Reflect the figure that we obtained in Step 1 across the y-axis
Hence,
The representation of the mapping of Figure A and Figure B using the above steps is:

Focus on math practices
Look for Relationships Is there another transformation or sequence of transformations that will map Figure A to Figure B?
Answer:
Yes, there are another sequence of transformations that will map Figure A to figure B
Now,
The steps to obtain Figure B from Figure A are:
Step 1:
Reflect Figure A across the y-axis
Step 2:
Reflect the figure that we obtained in Step 1 across the x-axis
Hence,
The representation of the mapping of Figure A and Figure B using the above steps is:

Essential Question
How can you use a sequence of transformations to map a preimage to its image?
Answer:
Mathematical transformations involve changing an image in some prescribed manner. There are four main types of transformations They are:
A) Translation B) Rotation C) Reflection D) Dilation

Try It!

Ava decided to move the cabinet to the opposite wall. What sequence of transformations moves the cabinet to its new position?

Answer:
It is given that
Ava decided to move the cabinet to the opposite wall
So,
From the figure,
We can observe that
To move the cabinet wall to the opposite wall, the following sequences of transformations have to be followed:
Step 1:
Translate the cabinet 8 units down
Step 2:
Rotate the cabinet 360° counterclockwise
Hence, from the above,
We can conclude that
The new position of the cabinet is:

Convince Me!
Ava decides that she would like the chairs to be placed directly across from the couch. What is a sequence of transformations that she can use to move the chairs to their new positions?

Try It!

What is another sequence of transformations that maps △ABC onto △A” B” C”?

Answer:
The given coordinate plane is:

From the given coordinate plane,
The vertices of ΔABC are:
A (-5, 5), B (-3, 3), and C (-6, 1)
Now,
Another sequence of transformations that maps ΔABC onto ΔA”B” C” is:
Step 1:
Draw ΔABC and make its reflection across the y-axis and name it ΔA’B’C’
Step 2:
Translate ΔA’B’C’ 2 units to the right and 6 units down
Step 3:
Reflect the figure we obtained in step 2 across the y-axis
Hence, from the above,
We can conclude that
The representation of another sequence of transformations that maps ΔABC onto ΔA”B” C” is:

KEY CONCEPT
You can use a sequence of two or more transformations to map a preimage to its image.
You can map △ABC onto △Α” Β” C” by translation of 3 units right followed by a 90° clockwise rotation about the origin.
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 51

Do You Understand?
Question 1.
Essential Question How can you use a sequence of transformations to map a preimage to its image?
Answer:
Mathematical transformations involve changing an image in some prescribed manner. There are four main types of transformations They are:
A) Translation B) Rotation C) Reflection D) Dilation

Question 2.
Make Sense and Persevere A preimage is rotated 180° about the origin and then rotated 180° about the origin again. Compare the preimage and image.
Answer:
It is given that
A preimage is rotated 180° about the origin and then rotated 180° about the origin again
Now,
When the preimage is rotated 180° and again 180°
The image will be the same as the preimage
Hence, from the above,
We can conclude that
When a preimage is rotated 180° about the origin and then rotated 180° about the origin again, the preimage and the image will be the same

Question 3.
Reasoning A figure ABC, with vertices A(2, 1), B(7, 4), and C(2, 7), is rotated 90° clockwise about the origin, and then reflected across the x-axis. Describe another sequence that would result in the same image.
Answer:
It is given that
A figure ABC, with vertices A(2, 1), B(7, 4), and C(2, 7), is rotated 90° clockwise about the origin, and then reflected across the x-axis
So,
The steps for another sequence of transformations that would result in the same image as the given situation is:
Step 1:
Draw the given vertices of Triangle ABC
Step 2:
Rotate Triangle ABC 90° counterclockwise
Step 3:
Reflect the image that we obtained in step 2 across the x-axis so that we will get the same image as in the given situation
Hence,
The representation of another sequence of transformations is:

Do You Know How?
In 4-6, use the diagram below.
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 52
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 52
From the given coordinate plane,
The vertices of Figure WXYZ are:
W (2, 4), X (5, 4), Y (5, 2), and Z (2, 2)
The vertices of Figure W’X’Y’Z’ are:
W’ (-4, -4), X’ (-4, -1), Y’ (-2, -1), and Z’ (-2, -4)

Question 4.
Describe a sequence of transformations that maps rectangle WXYZ onto rectangle W’X’Y’Z’.
Answer:
The steps that we have to follow to obtain the given sequence of transformations that maps rectangle WXYZ onto rectangle W’X’Y’Z’ are:
Step 1:
Draw rectangle WXYZ
Step 2:
Reflect rectangle WXYZ across the x-axis
Step 3:
Rotate the image we obtained in step 2 90° counterclockwise
Step 4:
Translate the image we obtained in step-3 6 units left so that we can obtain rectangle W’X’Y’Z’
Hence,
The representation of the sequence of transformations for the given situation is:

Question 5.
Describe another way that you could map rectangle WXYZ onto W’X’Y’Z’.
Answer:
The steps for another way of transformations that maps rectangle WXYZ onto W’X’Y’Z’ are:
Step 1:
Draw Rectangle WXYZ
Step 2:
Rotate rectangle WXYZ 90° counterclockwise
Step 3:
Rotate the image we obtained in step-2 180° counterclockwise
Step 4:
Translate the image we obtained in step 3 6 units down so that we can obtain rectangle W’X’Y’Z’
Hence,
The representation of another sequence of transformations is:

Question 6.
Draw the image of rectangle WXYZ after a reflection across the line y = 1 and a translation 1 unit right. Label the image W” X” Y” Z”.
Answer:
The vertices of rectangle WXYZ are:
W (2, 4), X (5, 4), Y (5, 2), and Z (2, 2)
After the reflection across the line y = 1,
The vertices of rectangle WXYZ are:
W’ (2, -5), X’ (5, -5), Y’ (5, -3), and Z’ (2, -3)
After the translation of 1 unit right,
The vertices of rectangle WXYZ are:
W” (3, -5), X” (6, -5), Y” (6, -3), and Z” (3, -3)
Hence,
The representation of rectangle WXYZ and its image W”X” Y”Z” after the above sequence of transformations is:

Practice & Problem Solving

Question 7.
Leveled Practice Describe a sequence of transformations that maps △QRS onto △TUV.
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 53
A translation ________ units left and ________ units down, followed by a _________ across the ________.
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 53
From the given coordinate plane,
The vertices of ΔQRS are:
Q (3, 4), R (7, 4), and S (6, 9)
The vertices of ΔTUV are:
T (0, 0), U (-4, 0), and V (-3, 5)
Now,
In order to obtain the vertices of ΔTUV, the following transformations we have to follow are:
Step 1:
Translate the vertices of ΔQRS 3 units left and 4 units down
Step 2:
Reflect the image we obtained in step 1 across the x-axis in order to get the vertices of ΔTUV
Hence, from the above,
We can conclude that
A translation of 3 units left and 4 units down, followed by a reflection across the x-axis

Question 8.
Model with Math
A family moves a table, shown as rectangle EFGH, by translating it 3 units left and 3 units down followed by a 90° rotation about the origin. Graph E’ F’G’H’ to show the new location of the table.
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 54
Answer:
It is given that
A family moves a table, shown as rectangle EFGH, by translating it 3 units left and 3 units down followed by a 90° rotation about the origin
Now,
The given coordinate plane is:
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 54
From the given coordinate plane,
The vertices of rectangle EFGH are:
E (3, 3), F (8, 3), G (8, 7), and H (3, 7)
Now,
To obtain rectangle E’F’G’H’,
The following series of transformations are:
Step 1:
By translating 3 units left and 3 units down,
The vertices of rectangle EFGH will become:
E (3 – 3, 3 – 3), F (8 – 3, 3 – 3), G (8 – 3, 7 – 3), and H (3 – 3, 7 – 3)
E (0, 0), F (5, 0), G (5, 4), and H (0, 4)
Step 2:
Rotate the vertices we obtain in step 1 90° counterclockwise about the origin
We know that,
When we rotate a point 90° counterclockwise about the origin,
(x, y) before rotation ——> (-y, x) after rotation
So,
The vertices of rectangle E’F’G’H’ are:
E’ (0, 0), F’ (0, 5), G’ (-4, 5), and H’ (-4, 0)
Hence,
The representation of the new location of the table is:

Question 9.
Describe a sequence of transformations that maps quadrilateral ABCD to quadrilateral HIJK.
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 55
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 55
From the given coordinate plane,
The vertices of quadrilateral ABCD are:
A (3, 1), B (4, 1), C (4, 3), and D (3, 3)
The vertices of quadrilateral HIJK are:
H (-3, 0), I (-2, 0), J (-2, -2), and K (-3, -2)
Now,
The series of transformations that maps quadrilateral ABCD onto quadrilateral HIJK are:
Step 1:
Draw quadrilateral ABCD
Step 2:
Reflect quadrilateral ABCD across the x-axis
So,
The vertices of quadrilateral ABCD are:
A (3, -1), B (4, -1), C (4, -3), and D (3, -3)
Step 3:
Translate 6 units left and 1 unit up
So,
The vertices that we obtained in step 2 will become (The vertices of quadrilateral HIJK):
H (-3, 0), I (-2, 0), J (-2, -2), and K (-3, -2)
Hence,
The representation of the series of transformations that map quadrilateral ABCD onto quadrilateral HIJK are:

Question 10.
Map △QRS to △Q’R’ S’with a reflection across the y-axis followed by a translation 6 units down.
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 56
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 56
From the given coordinate plane,
The vertices of ΔQRS are:
Q (-3, 5), R (-2, 4), and S (-5, 3)
Now,
The series of transformations that maps ΔQRS to ΔQ’R’S’ as given above are:
Step 1:
Reflect the vertices of ΔQRS along the y-axis
So,
Q (3, 5), R (2, 4), and S (5, 3)
Step 2:
Translate the vertices that we obtain in step-1 6 units down so that we can obtain the vertices of ΔQ’R’S’
So,
Q’ (3, 5 – 6), R’ (2, 4 – 6), and S’ (5, 3 – 6)
Q’ (3, -1), R’ (2, -2), and S’ (5, -3)
Hence,
The representation of the series of transformations for the given situation is:

 

Question 11.
Higher-Order Thinking A student says that he was rearranging furniture at home and he used a glide reflection to move a table with legs from one side of the room to the other. Will a glide reflection result in a functioning table? Explain.
Answer:
It is given that
A student says that he was rearranging furniture at home and he used a glide reflection to move a table with legs from one side of the room to the other.
We know that,
A glide reflection is a  sequence of translation and reflection
Now,
From the given situation,
We can observe that the table is moving from one room to the other
So,
The “Translation” occurs
Now,
After moving he will rearrange the table in the room
So,
A “Reflection” may take place
Hence, from the above,
We can conclude that a glide reflection result in a functioning table

Assessment Practice
Question 12.
PART A
Which sequence of transformations maps rectangle ABCD onto rectangle A’ B’C’D?
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 57
A. translation 6 units down, reflection across the x-axis
B. reflection across the x-axis, translation 6 units right
C. reflection across the x-axis, translation 6 units left
D. translation 6 units left, reflection across the y-axis
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 57
From the given coordinate plane,
The vertices of rectangle ABCD are:
A (2, -2), B (4, -2), C (4, -3), and D (2, -3)
The vertices of rectangle A’B’C’D’ are:
A’ (-4, 2), B’ (-2, 2), C’ (-2, 3), and D’ (-4, 3)
So,
The sequence of transformations that maps rectangle ABCD to rectangle A’B’C’D’ is:

Hence, from the above,
We can conclude that option C matches the given situation

PART B
Describe a sequence of transformations that maps A’B’C’ D’ onto ABCD.
Answer:
The sequence of transformations that maps A’B’C’D’ onto ABCD is:
Step 1:
Draw the rectangle ABCD
So,
The vertices of rectangle ABCD are:
A (2, -2), B (4, -2), C (4, -3), and D (2, -3)
Step 2:
Reflect rectangle ABCD across the x-axis
So,
The vertices of rectangle ABCD are:
A (2, 2), B (4, 2), C (4, 3), and D (2, 3)
Step 3:
Translate the vertices that we obtained in step 2 6 units left so that we can obtain rectangle A’B’C’D’
So,
A’ (2 – 6, 2), B’ (4 – 6, 2), C’ (4 – 6, 3), and D’ (2 – 6, 3)
So,
A’ (-4, 2), B’ (-2, 2), C’ (-2, 3), and D’ (-4, 3)

Question 13.
PART A
Which figures are the image of Figure A after a reflection across the x-axis and a translation of 4 units right?
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 58
A. Figure B
B. Figure C
C. Figure D
D. Figure E
Answer:
We know that,
A “Reflection” is called a “Flip” but the reflection does not affect the shape and length of the figure
So,
From the given figures,
When we observe Figures A and B,
We can say that Figure B is a reflection of A because the shape and length is the same
But,
when we observe the other figures,
We have different shapes and lengths between the preimage and the image
Hence, from the above,
We can conclude that
Figure B is the image of Figure A after a reflection across the x-axis and a translation of 4 units right

PART B
Which figure can be transformed into Figure G after a rotation 90° about the origin, then a translation 13 units right and 4 units down?
A. Figure B
B. Figure D
C. Figure E
D. Figure F
Answer:
From the given figures,
We have to obtain
The coordinates of Figure G are:
(6, -6), (9, -6), (9, -9), (7, -9), and (6, -5)
We know that,
When a point rotates 90° about the origin,
(x, y) before rotation ——-> (-y, x) after rotation
Now,
For the translation of 13 units right and 4 units down,
The vertices will be like: (x + 13, y – 4)
Hence, from the above,
We can conclude that option A matches the given situation

3-ACT MATH

3-Act Mathematical Modeling: Tricks of the Trade
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 59

ACT 1
Question 1.
After watching the video, what is the first question that comes to mind?
Answer:

Question 2.
Write the Main Question you will answer.
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 60
Answer:

Question 3.
Make a prediction to answer this Main Question.
Answer:

Question 4.
Construct Arguments Explain how you arrived at your prediction.
Answer:

ACT 2
Question 5.
What information in this situation would be helpful to know? How would you use that information?
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 61
Answer:

Question 6.
Use Appropriate Tools What tools can you use to solve the problem? Explain how you would use them strategically.
Answer:

Question 7.
Model with Math Represent the situation using mathematics. Use your representation to answer the Main Question.
Answer:

Question 8.
What is your answer to the Main Question? Does it differ from your prediction? Explain.
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 62
Answer:

ACT 3
Question 9.
Write the answer you saw in the video.
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 63
Answer:

Question 10.
Reasoning Does your answer match the answer in the video? If not, what are some reasons that would explain the difference?
Answer:

Question 11.
Make Sense and Persevere Would you change your model now that you know the answer? Explain.
Answer:

ACT 3 Extension
Reflect
Question 12.
Model with Math Explain how you used a mathematical model to represent the situation. How did the model help you answer the Main Question?
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 64
Answer:

Question 13.
Make Sense and Persevere When did you struggle most while solving the problem? How did you overcome that obstacle?
Answer:

SEQUEL
Question 14.
Be Precise Find another optical illusion online involving shapes that look different but are the same. Explain how you know the shapes are the same.
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 65
Answer:

Lesson 6.5 Understand Congruent Figures

Solve & Discuss It!
Simone plays a video game in which she moves shapes into empty spaces. After several rounds, her next move must fit the blue piece into the dashed space. How can Simone move the blue piece to fit in the space?
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 66
I can… use a sequence of translations, reflections, and rotations to show that figures are congruent.
Answer:
It is given that
Simone plays a video game in which she moves shapes into empty spaces. After several rounds, her next move must fit the blue piece into the dashed space.
Now,
From the given figure,
We can observe that
The blue piece and the dashed  piece are the reflections of each other
Hence,
Simone move the blue piece to fit in the space by the translation followed by reflection

Reasoning
How can you use what you know about sequences of transformations to move the piece?
Answer:
From the given figure,
We can observe that
The blue piece should be moved to the place of the dashed space and it will be possible only due to the “Translation”
But,
We can observe that it does not fit into the dashed space.
So,
Reflect the blue piece that it can fit into the dashed piece
Hence, from the above,
We can conclude that the sequence of transformations we can use to move the transformation are:
a. Translation b. Reflection

Focus on math practices
Construct Arguments How do you know that the piece that fits into the space is the same as the original blue shape? Explain.
Answer:
We know that,
In the reflection,
a. The shape of the preimage and the image are the same
b. The length of the preimage and the image are the same
c. The orientation of the image and the preimage are different
Hence, from the above,
We can conclude that
Due to the properties of the reflection,
We know that the piece that fits into space is the same as the original shape

Essential Question
How does a sequence of translations, reflections, and rotations result in congruent figures?
Answer:
If we copy one figure on tracing paper and move the paper so the copy covers the other figure exactly, then that suggests they are congruent. We can prove that two figures are congruent by describing a sequence of translations, rotations, and reflections that move one figure onto the other so they match up exactly.

Try It!

How can you determine whether the orange and blue rectangles are congruent?
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 67
Answer:
The given coordinate plane is:

From the given coordinate plane,
We can observe that
The blue rectangle has a length of 6 units and a width of 5 units
The orange rectangle has a length of 5 units and a width of 6 units
Now,
We can say that
We can obtain the orange rectangle by rotating the blue rectangle
We know that,
Rotations, reflections, and translations are isometric. That means that these transformations do not change the size of the figure. If the size and shape of the figure is not changed, then the figures are congruent
Hence, from the above,
We can conclude that the orange and blue rectangles are congruent

Convince Me!
Quadrilateral PQRS is congruent to quadrilateral P’ Q’R’S. What do you know about how these figures relate?
Answer:
It is given that
Quadrilateral PQRS is congruent to quadrilateral P’ Q’R’S
We know that,
When the two figures are congruent,
a. The shapes of the two figures are the same
b. The lengths of the two figures are the same
c. The angle measures of the two figures are the same
Hence,
In Quadrilateral PQRS and Quadrilateral P’Q’R’S’, the two figures are said to be congruent when
a. PQ = P’Q’ and RS = R’S’
b. ∠P = ∠P’, ∠Q = ∠Q’, ∠R = ∠R’, and ∠S = ∠S’

Try It!

Are the figures congruent? Explain.
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 68
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 68
From the given coordinate plane,
The vertices of Figure 1 are:
(1, 5), (3, 7), (3, 5), and (2, 3)
The vertices of Figure 2 are:
(6, 3), (8, 3), (10, 2), and (8, 1)
Now,
Find out whether Translation, Reflection, and Rotation is possible between 2 figures or not
So,
The representation of Figure 1 and Figure 2 are:

Now,
From the given figures,
We can observe that none of the transformations is possible
Hence, from the above,
We can conclude that the two figures are not congruent

KEY CONCEPT

Two-dimensional figures are congruent if there is a sequence of translations, reflections, and rotations that maps one figure onto the other.
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 69

Do You Understand?
Question 1.
Essential Question How does a sequence of translations, reflections, and rotations result in congruent figures?
Answer:
If we copy one figure on tracing paper and move the paper so the copy covers the other figure exactly, then that suggests they are congruent. We can prove that two figures are congruent by describing a sequence of translations, rotations, and reflections that move one figure onto the other so they match up exactly.

Question 2.
Reasoning Does a sequence of transformations have to include a translation, a reflection, and a rotation to result in congruent figures? Explain.
Answer:
Rotations, reflections, and translations are isometric. That means that these transformations do not change the size of the figure. If the size and shape of the figure is not changed, then the figures are congruent

Question 3.
Construct Arguments Is there a sequence of reflections, rotations, and translations that makes the preimage and image not only congruent, but identical in orientation? Explain.
Answer:
We know that,
In the reflection,
The orientation of the preimage and the image will differ
Hence, from the above,
We can conclude that
There is a sequence of reflections, rotations, and translations that makes the preimage and image only congruent but not identical in orientation

Do You Know How?
Question 4.
A rectangle with an area of 25 square centimeters is rotated and reflected in the coordinate plane. What will be the area of the resulting image? Explain.
Answer:
It is given that
A rectangle with an area of 25 square centimeters is rotated and reflected in the coordinate plane.
We know that,
In a sequence of transformations like Translation, Rotation, and Reflection,
The shapes and side lengths of the image and the preimage are the same
Since the side lengths are the same, the area will also be the same
Hence, from the above,
We can conclude that the area of the image will also be 25 square centimeters

In 5 and 6, use the coordinate grid below.
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 70
Answer:
The given coordinate plane is:
Envision Math Common Core 8th Grade Answers Topic 6 Congruence And Similarity 70
From the given coordinate plane,
The vertices of ΔABC are:
A (1, 4), B (2, 2), and C (5, 2)
The vertices of ΔDEF are:
D (9, 9), E (8, 7), and F (5, 7)
The vertices of ΔGHI are:
G (6, 6), H (8, 5), and I (8, 1)

Question 5.
Is △ABC ≅ △DEF? Explain.
Answer:
To find whether ΔABC is congruent to ΔDEF or not,
Step 1:
Reflect Triangle ABC across the x-axis
Step 2:
Translate the image that we obtained in step-1 10 units right and 5 units up
So,
The representation of step 1 and step 2 is:

Hence, from the above,
We can observe that the vertices we obtained in step 2 are the same as ΔDEF
Hence,
ΔABC is congruent to ΔDEF

Question 6.
Is △ABC ≅ △GHI? Explain.
Answer:
The representation of △ABC and △GHI is:

From the above,
We can observe that △ABC and △GHI do not have the same size
We know that,
In order to be 2 figures congruent,
a. The sizes of the figures would be the same
b. The shapes of the figures would be the same
c. The side lengths of the figures should be the same
Hence, from the above,
We can conclude that
△ABC is not congruent to △GHI

Practice & Problem Solving

Question 7.
△Q’R’ S’ is the image of △QRS after a reflection across the y-axis and a translation 6 units down. Is the image the same size and shape as the preimage?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 71
△QRS and △Q’R’S’ _________ the same size and shape.
Answer:
It is given that
△Q’R’ S’ is the image of △QRS after a reflection across the y-axis and a translation 6 units down
Now,
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 71
From the given coordinate plane,
The vertices of ΔQRS are:
Q (-3, 5), R (-2, 4), and S (-5, 3)
The vertices of ΔQ’R’S’ are:
Q’ (3, -1), R’ (2, -2), and S’ (5, -3)
Now,
Step 1:
After a reflection of ΔQRS across the y-axis,
The vertices of ΔQRS will be:
Q (3, 5), R (2, 4), and S (5, 3)
Step 2:
After a translation of 6 units down,
The vertices that we obtained in Step 1 are:
Q’ (3, 5 – 6), R’ (2, 4 – 6), and S’ (5, 3 – 6)
Q’ (3, -1), R’ (2, -2), and S’ (5, -3)
So,
The vertices of ΔQ’R’S’ we obtained from the coordinate plane and the vertices of ΔQ’R’S’ we obtained after the sequence of transformations are the same
Hence, from the above,
We can conclude that △QRS and △Q’R’S’ have the same size and shape and the image (ΔQ’R’S’) is the same size and shape as the preimage (ΔQRS)

Question 8.
Is △DEF ≅ △D’ E’F’? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 72
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 72
From the given coordinate plane,
The vertices of ΔDEF are:
D (5, 5), E (6, 3), and F (2, 4)
The vertices of ΔD’E’F’ are:
D’ (-2, -1), E’ (-3, 1), and F’ (1, 0)
So,
The representtaion of the sequence of transformations of ΔDEF to show it is congruent to ΔD’E’F’ is:

Hence, from the above,
We can conclude that ΔDEF is congruent to ΔD’E’F’

Question 9.
Construct Arguments Describe a way to show that quadrilateral ABCD is congruent to quadrilateral A’B’C’D’.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 73
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 73
From the given coordinate plane,
The vertices of quadrilateral ABCD are:
A (3, 5), B (5, 5), C (5, 4), and D (3, 4)
The vertices of quadriateral A’B’C’D’ are:
A’ (-3, 0), B’ (-5, 0), C’ (-5, -1), and D’ (-3, -1)
So,
The representtaion of the transformation of sequences that shows quadrilateral ABCd is congruent to quadrilateral A’B’C’D’ is:

Hence, from the above,
We can conclude that quadrilateral ABCD is congruent to quadrilateral A’B’C’D’

Question 10.
You are making two triangular flags for a project and need the flags to be the same shape and size. △XYZ and △X’Y’Z’ are the flags you have drawn. Are the flags the same shape and size? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 74
Answer:
It is given that
You are making two triangular flags for a project and need the flags to be the same shape and size. △XYZ and △X’Y’Z’ are the flags you have drawn.
Now,
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 74
From the given coordiate plane,
The vertices of ΔXYZ are:
X (5, 6), Y (6, 1), and Z (2, 2)
he vertices of ΔX’Y’Z’ are:
X’ (-2, 0), Y’ (-3, -5), and Z’ (1, -4)
So,
The representtaion of the sequence of transformation to find whether two flags have the same size and the same shape or not is:

Question 11.
Which two triangles are congruent? Describe the sequence of transformations that maps one figure onto the other.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 75
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 75
From the given coordinate plane,
The vertices of ΔABC are:
A (-3, 2), B (-2, 7), and C (-7, 4)
The vertices of ΔQRS are:
Q (4, 7), R (2, 2), and S (7, 2)
The vertices of ΔXYZ are:
X (-2, -7), Y (-2, -3), and Z (-7, -5)
The vertices of ΔDEF are:
D (7, -5), E (2, -2), and F (2, -7)
Now,
We know that,
The two figures are said to be congruent when
a. The 2 figures have the same size i.e., the same length and the same angle measure
b. The 2 figures have the same shape
So,
The figures that are congruent to each other are represented as:

So,
From the above,
We can say that ΔQRS and ΔDEf are congruent
Hence,
The sequence of Transformations to show ΔQRS and ΔDEF are congruent is:

Question 12.
Is △LMN ≅ △XYZ? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 76
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 76
From the given coordinate plane,
The vertices of ΔLMN are:
L (7, 9), M (9, 5), and N (6, 5)
The vertices of ΔXYZ are:
X (2, 2), Y (5, 4), and Z (5, 1)
Now,
We know that,
The two figures are said to be congruent when
a. The 2 figures have the same size i.e., the same length and the same angle measure
b. The 2 figures have the same shape
So,
The sequence of transformations to find whether ΔLMN is congruent to ΔXYZ is:

Hence, from the above,
We can conclude that ΔLMN is not congruent to ΔXYZ since they don’t have the same side lengths

Question 13.
Higher-Order Thinking A student was asked to describe a sequence of transformations that maps △DEF onto △D’ E’F’, given that △DEF ≅ △D’ E’F’. She incorrectly said the sequence of transformations that maps △DEF onto △D’ E’F’ is a reflection across the x-axis, followed by a translation of 6 units right and 4 units up. What mistake did the student likely make?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 77
Answer:
It is given that
A student was asked to describe a sequence of transformations that maps △DEF onto △D’ E’F’, given that △DEF ≅ △D’ E’F’. She incorrectly said the sequence of transformations that maps △DEF onto △D’ E’F’ is a reflection across the x-axis, followed by a translation of 6 units right and 4 units up
Now,
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 77
From the given coordinate plane,
The vertices of ΔDEF are:
D (4, 5), E (5, 1), and F (1, 2)
The vertices of ΔD’E’F’ are:
D’ (-2, -1), E’ (-1, 3), and F’ (-5, 2)
Now,
The correct sequence of Transformations to show ΔDEF and ΔD’E’F’ are congruent is:

Hence, from the above,
We can conclude that the mistake done by a student is the interchange of the sequence of Transformations
Hence,
The correct sequence of Transformations is:
Translation of 6 units left and 4 units down followed by the reflection across the x-axis

Assessment Practice
Question 14.
PART A
How can you determine whether △DEF ≅ △D’ E’ F?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 78
A. Determine whether a sequence of rotations maps △DEF onto △D’E’F’.
B. Determine whether a sequence of transformations maps △DEF onto △D’ E’F’.
C. Determine whether a sequence of translations maps △DEF onto △D’ E’F’.
D. Determine whether a sequence of reflections maps △DEF onto △D’ E’F’.
Answer:
We know that,
If we want to find whether the given figures are congruent or not, then
We have to determine whether a sequence of transformations maps ΔDEF onto ΔD’E’F’
Hence, from the above,
We can conclude that option A matches the given situation

PART B
Is △DEF ≅ △D’ E’ F? Explain.
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 78
From the given coordinate plane,
The vertices of ΔDEF are:
D (5, 5), E (6, 3), and F (2, 4)
The vertices of ΔD’E’F’ are:
D’ (-2, -1), E’ (-3, 1), and F’ (1, 0)
So,
The representation of the sequence of transformations to find out whether ΔDEf and ΔD’E’F’ are congruent or not is:

Hence, from the above,
We can conclude that ΔDEF is congruent to ΔD’E’F’

Topic 6 MID-TOPIC CHECKPOINT

Question 1.
Vocabulary Describe three transformations where the image and preimage have the same size and shape. Lesson 6-1, Lesson 6-2, and Lesson 6-3
Answer:
We know that,
There are four types of transformations. They are:
a. Translation
b. Reflection
c. Rotation
d. Translation
Now,
Some transformations keep the pre-image and image congruent. Congruent means that they are the same size and shape or that they have the same measurements. They make not have the same orientation
Hence,
Three of the four transformations that preserve the size and shape of the pre-image are: Translation, Rotation, and Reflections

For 2-6, use the figures below.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 79
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 79
From the given coordinate plane,
The vertices of the quadrilateral MNPQ are:
M (1, 2), N (2, 4), P (4, 5), and Q (3, 3)
The vertices of the quadrilateral RSTU are:
R (1, -2), S (2, -4), T (4, -5), and U (3, -3)

Question 2.
What are the coordinates of each point after quadrilateral RSTU is rotated 90° about the origin? Lesson 6-3
Answer:
We know that,
When any point is rotated 90° about the origin,
(x, y) before rotation ——–> (-y, x) after rotation
Hence,
After 90° rotation about the origin,
The coordinates of each point of the quadrilateral RSTU will become:
R (2, 1), S (4, 2), T (5, 4), and U (3, 3)

Question 3.
What are the coordinates of each point after quadrilateral MNPQ is translated 2 units right and 5 units down? Lesson 6-1
Answer:
We know that,
When the translation occurs,
(x, y) before Translation ——-> (x + h, y + k) after Translation
Where,
h is the translation on the x-axis
k is the translation on the y-axis
We will take the positive value of h when the translation occurs on the right side of the x-axis
We will take the negative value of h when the translation occurs on the left side of the x-axis
We will take the positive value of k when the translation occurs on the top side of the y-axis
We will take the negative value of k when the translation occurs on the down side of the y-axis
Hence,
After the Translation of 2 units right and 5 units down,
The coordinates of each point of the quadrilateral MNPQ will become:
M (1 + 2, 2 – 5), N (2 + 2, 4 – 5), P (4 + 2, 5 – 5), and Q (3 + 2, 3 – 5)
M (3, -3), N (4, -1), P (6, 0), and Q (5, -2)

Question 4.
What are the coordinates of each point after quadrilateral MNPQ is reflected across the x-axis and then translated into 3 units left? Lessons 6-2 and 6-4
Answer:
We know that,
The vertices of the quadrilateral MNPQ are:
M (1, 2), N (2, 4), P (4, 5), and Q (3, 3)
So,
After the vertices of the quadrilateral, MNPQ reflected across the x-axis,
The vertices of the quadrilateral MNPQ will become:
M (1, -2), N (2, -4), P (4, -5), and Q (3, -3)
Now,
After the Translation of 3 units left,
The vertices of the quadrilateral MNPQ will become:
M (1 – 3, -2), N (2 – 3, -4), P (4 – 3, -5), and Q (3 – 3, -3)
M (-2, -2), N (-1, -4), P (1, -5), and Q (0, -3)
Hence, from the above,
We can conclude that the coordinates of each point after quadrilateral MNPQ is reflected across the x-axis and then translated into 3 units left are:
M (-2, -2), N (-1, -4), P (1, -5), and Q (0, -3)

Question 5.
Which series of transformations maps quadrilateral MNPQ onto quadrilateral RSTU? Lesson 6-4
A. reflection across the x-axis, translation 4 units down
B. reflection across the y-axis, translation 4 units down
C. rotation 180° about the origin, and then reflection across the x-axis
D. rotation 180° about the origin, and then reflection across the y-axis
Answer:
The representation of the series of transformations that maps the quadrilateral MNPQ onto the quadrilateral RSTU is:

Hence, from the above,
We can conclude that option A matches the given situation

Question 6.
Is quadrilateral MNPQ congruent to quadrilateral RSTU? Explain. Lesson 6-5
Answer:
We know that,
The 2 figures are said to be congruent only when:
a. The shapes of the 2 figures are the same
b. The sizes of the 2 figures are the same (Side lengths, and Angle measures)
Now,

From the above,
We can observe that the side lengths are not the same
Hence, from the above,
We can conclude that the quadrilateral MNPQ is not congruent to the quadrilateral RSTU

Topic 6 MID-TOPIC PERFORMANCE TASK

A tessellation is a design in a plane that uses one or more congruent figures, with no overlaps and no gaps, to cover the entire plane. A tessellation of an equilateral triangle is shown.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 80

PART A
Explain how the tessellation of an equilateral triangle is formed using reflections.
Answer:
We know that,
When you cut a shape out of paper, then flip it over, the flipped shape looks like a mirror image of the original shape. So a tessellation made with this technique is called a “Reflection tessellation”
Now,
See if the figure will fit together with no gaps. The answer is yes, the figures will tessellate because it is made up of two shapes that do tessellate

PART B
Explain how the tessellation of an equilateral triangle is formed using rotations.
Answer:
We know that
A “Rotational tessellation” is a pattern where the repeating shapes fit together by rotating 90 degrees
Now,
See if the figure will fit together with no gaps. The answer is yes, the figures will tessellate because it is made up of two shapes that do tessellate

PART C
Which of the regular polygon(s) below can be tessellated using a series of transformations?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 81
Answer:
We know that,
Equilateral triangles, squares, and regular hexagons are the only regular polygons that will tessellate. Therefore, there are only three regular tessellations.
Hence, from the above,
We can conclude that square and pentagon can be tessellated by using a series of transformations

Lesson 6.6 Describe Dilations

Solve & Discuss It!
A landscape architect designs a small splash pad represented by △ABC. Then she decides to make the splash pad larger as shown by △ADE. How are the splash pad designs alike? How are they different?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 82
I can… dilate two-dimensional figures
Answer:
It is given that
A landscape architect designs a small splash pad represented by △ABC. Then she decides to make the splash pad larger as shown by △ADE.
Now,
The given landscape architect is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 82
Now,
From the given landscape architect,
We can observe that the difference in the splash designs
Hence, from the above landscape architect,
We can conclude that
The splash designs are alike in:
a. Shape b. Angle measures c. Orientation
The splash designs are different in:
a. Side lengths

Look for Relationships
How can you use what you know about scale drawings to compare and contrast the designs?
Answer:
A dilation is a transformation that results in an image with the same shape, angle measures, and orientation as the preimage, but different side lengths.
We know that,
When the scale factor is greater than 1, the dilation is a reduction.
When the scale factor is between 0 and 1, the dilation is an enlargement.

Focus on math practices
Reasoning Paul wants to make two square picnic tables. One table will have side lengths that are \(\frac{1}{2}\) of the lengths of the second table. How do the tablets compare? Explain.
Answer:
It is given that
Paul wants to make two square picnic tables. One table will have side lengths that are \(\frac{1}{2}\) of the lengths of the second table
So,
The size of the tables are in the ratio of \(\frac{1}{2}\) : 1
So,
The size of the tables are in the ratio of 1:2
Hence, from the above,
We can conclude that the side lengths of one table are 2 times the side lengths of the second table

Essential Question
What is the relationship between a preimage and its image after a dilation?
Answer:
After dilation, the pre-image and image have the same shape but not the same size.
In terms of Sides:
In dilation, the sides of the pre-image and the corresponding sides of the image are proportional.

Try It!

F’G’ H’I’ is the image of FGHI after a dilation with center at the origin. What is the scale factor?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 83
The ratio of a side length in FGHI to a corresponding side length in F’GH’I’is: \(\frac{}{}\)
The scale factor is __________.
Answer:
It is given that
F’G’ H’I’ is the image of FGHI after a dilation with center at the origin.
Now,
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 83
From the given coordinate plane,
The vertices of FGHI are:
F (1, 1), G (1, 2), H (2, 2), and I (2, 1)
The vertices of F’G’H’I’ are:
F’ (5, 5), G’ (5, 10), H’ (10, 10), and I’ (10, 5)
We know that,
The “Scale factor” is the ratio of a length in the image to the corresponding length in the preimage
So,
The ratio of a side length in FGHI to a corresponding side length in F’GH’I’is:
\(\frac{Side length of F’G’}{Side length of FG}\) (or) \(\frac{Side length of H’I’}{Side length of HI}\)
= \(\frac{0 + 5}{0 + 1}\) (or) \(\frac{0 + 5}{0 + 1}\)
= 5
So,
The scale factor is: 5
Hence, from the above,
We can conclude that
The ratio of a side length in FGHI to a corresponding side length in F’GH’I’is: \(\frac{5}{1}\)
The scale factor is 5.

Convince Me!
Quadrilateral WXYZ is the image of quadrilateral FGHI after a dilation with center at the origin and a scale factor of 3.5. What are the coordinates of the vertices of quadrilateral WXYZ?
Answer:
It is given that
Quadrilateral WXYZ is the image of quadrilateral FGHI after a dilation with center at the origin and a scale factor of 3.5
Now,
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 83
From the given coordinate plane,
The vertices of FGHI are:
F (1, 1), G (1, 2), H (2, 2), and I (2, 1)
It is given that
The scale factor is: 3.5
So,
The vertices of the quadrilateral WXYZ are:
W ( 1 × 3.5, 1 ×3.5), X (1 × 3.5, 2 × 3.5), Y (2 × 3.5, 2 × 3.5), and Z (2 × 3.5, 1 × 3.5)
So,
W (3.5, 3.5), X (3.5, 7), Y (7, 7), and Z (7, 3.5)
Hence, from the above,
We can conclude that
The coordinates of the vertices of quadrilateral WXYZ are:
W (3.5, 3.5), X (3.5, 7), Y (7, 7), and Z (7, 3.5)

Try It!

A dilation maps point L(3, 6) to its image L’ (2, 4). Complete the dilation of figure LMN and label the image L’M’N’. What is the scale factor? What is the length of side M’N’?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 84
Answer:
It is given that
A dilation maps point L(3, 6) to its image L’ (2, 4). Complete the dilation of figure LMN and label the image L’M’N’
Now,
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 84
From the coordinate plane,
The vertices of ΔLMN are:
L (3, 6), M (3, 3), and N (6, 3)
It is given that the image of L is: L’ (2, 4)
Now,
We know that,
The “Scale factor” is the ratio of a length in the image to the corresponding length in the preimage
So,
The scale factor = \(\frac{Side length of L’}{Side length of L}\)
= \(\frac{4 – 2}{6 – 3}\)
= \(\frac{2}{3}\)
So,
The scale factor is: \(\frac{2}{3}\)
Now,
The coordinates of M’ = The coordinates of M × \(\frac{2}{3}\)
= (3, 3) × \(\frac{2}{3}\)
= (3 × \(\frac{2}{3}\), 3 × \(\frac{2}{3}\))
= (2, 2)
The coordinates of N’ = The coordinates of N × \(\frac{2}{3}\)
= (6, 3) × \(\frac{2}{3}\)
= (6 × \(\frac{2}{3}\), 3 × \(\frac{2}{3}\))
= (4, 2)
Now,
Compare M’ and N’ with (x 1, y 1), (x 2, y 2 )
We know that,
The distance between 2 points = √(x 2 – x 1 ) 2 + (y 2 – y 1 ) 2
So,
The side length of M’N’ = √(4 – 2 ) 2 + (2 – 2 )
= 2 units
Hence, from the above,
We can conclude that
The scale factor is: \(\frac{2}{3}\)
The side length of M’N’ is: 2 units

KEY CONCEPT

A dilation is a transformation that results in an image with the same shape, angle measures, and orientation as the preimage, but different side lengths.
When the scale factor is greater than 1, the dilation is an enlargement.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 85

When the scale factor is between 0 and 1, the dilation is a reduction.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 86

Do You Understand?
Question 1.
Essential Question What is the relationship between a preimage and its image after a dilation?
Answer:
After dilation, the pre-image and image have the same shape but not the same size.
In terms of Sides:
In dilation, the sides of the pre-image and the corresponding sides of the image are proportional.

Question 2.
Generalize When will a dilation be a reduction? When will it be an enlargement?
Answer:
When the scale factor is greater than 1, the dilation is an enlargement.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 85
When the scale factor is between 0 and 1, the dilation is a reduction.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 86

Question 3.
Reasoning Flora draws a rectangle with points at (12, 12), (15, 12), (15,9), and (12, 9). She dilates the figure with center at the origin and a scale factor of \(\frac{3}{4}\). what is the measure of each angle in the image? Explain.
Answer:
It is given that
Flora draws a rectangle with points at (12, 12), (15, 12), (15,9), and (12, 9). She dilates the figure with center at the origin and a scale factor of \(\frac{3}{4}\)
So,
The vertices for the image of the given rectangle = (x × \(\frac{3}{4}\), y × \(\frac{3}{4}\))
So,
The vertices for the image of the given rectangle wil be:
( 12 × \(\frac{3}{4}\), 12 × \(\frac{3}{4}\)), (15 × \(\frac{3}{4}\), 12 × \(\frac{3}{4}\)), (15 × \(\frac{3}{4}\), 9 × \(\frac{3}{4}\)), and (12 × \(\frac{3}{4}\), 9 × \(\frac{3}{4}\))
= (9, 9), (11.25, 9), (11.25, 6.75), and (9, 6.75)
Now,
We know that,
In dilation,
a. The preimage and image are the same in shape, orientation, and angle measures
b. the preimage and the image are different in size and the side lengths
So,
The representation of the angle measures in the preimage and image of the given rectangle is:

Hence, from the above,
We can conclude that the measure of each angle in the image is: 90°

Do You Know How?
In 4-6, use the coordinate grid below.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 87
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 87
From the coordinate plane,
The vertices of Figure 1 are:
(4, 4), (6, 8), and (8, 4)
The vertices of Figure 2 are:
(2, 2), (3, 4), and (4, 2)
The vertices of Figure 3 are:
(1, 1), (1.5, 2), and (2, 1)

Question 4.
Figure 3 is the image of Figure 1 after a dilation with a center at the origin. What is the scale factor? Explain.
Answer:
It is given that
Figure 3 is the image of Figure 1 after a dilation with a center at the origin
Now,
We know that,
The “Scale factor” is the ratio of a length in the image to the corresponding length in the preimage
So,
Scale factor = \(\frac{4}{1}\) (or) \(\frac{6}{1.5}\) (or) \(\frac{8}{2}\)
= 4
Hence, from the above,
We can conclude that the scale factor is “4” so that Figure 3 is the image of Figure 1

Question 5.
What are the coordinates of the image of Figure 2 after a dilation with center at the origin and a scale factor of 3?
Answer:
We know that,
The vertices of Figure 2 are:
(2, 2), (3, 4), and (4, 2)
So,
With a scale factor of 3,
The vertices of Figure 2 will become:
(2 × 3, 2 × 3), (3 × 3, 4 × 3), and (4 × 3, 2 × 3)
= (6, 6), (9, 12), and (12, 6)
Hence, from the above,
We can conclude that the coordinates of the image of Figure 2 after a dilation at the origin and a scale factor of 3 are:
(6, 6), (9, 12), and (12, 6)

Question 6.
Which figures represent a dilation with a scale factor of \(\frac{1}{2}\)?
Answer:
We know that,
The vertices of Figure 1 are:
(4, 4), (6, 8), and (8, 4)
The vertices of Figure 2 are:
(2, 2), (3, 4), and (4, 2)
The vertices of Figure 3 are:
(1, 1), (1.5, 2), and (2, 1)
Now,
If we consider Figure 2 as the preimage and Figure 1 as the image, then
Scale factor = \(\frac{2}{4}\) (or) \(\frac{3}{6}\) (or) \(\frac{4}{8}\)
= \(\frac{1}{2}\)
If we consider Figure 3 as the preimage and Figure 2 as the image, then
Scale factor = \(\frac{1}{2}\) (or) \(\frac{1.5}{3}\) (or) \(\frac{2}{4}\)
= \(\frac{1}{2}\)
Hence, from the above,
We can conclude that (Figure 2, Figure 1) and (Figure 3, Figure 2) represent a dilation with a scale factor of \(\frac{1}{2}\)

Practice & Problem Solving

Question 7.
Leveled Practice Draw the image of △DEF after a dilation with center (0, 0) and scale factor of 2.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 88
Find the coordinates of each point in the original figure.
D(____, (____) E(____, (____) F(____, (____)
Multiply each coordinate by _______.
Find the coordinates of each point in the image:
D'(____, (____) E'(____, (____) F'(____, (____)
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 88
Now,
From the given coordinate plane,
The vertices of ΔDEF are:
D (0, 0), E (2, 0), and F (0, 2)
Now,
With a scale factor of 2,
Multiply each coordinate with 2
The coordinates of ΔDEF will become:
D (0 × 2, 0 × 2), E (2 × 2, 0 × 2), and F (0 × 2, 2 × 2)
D (0, 0), E (4, 0), and F (0, 4)
So,
The coordinates of the points for the image of ΔDEF are:
D’ (0, 0), E’ (4, 0), and F’ (0, 4)
Hence,
The representation of ΔDEF and its image ΔD’E’F’ is:

Question 8.
Find the scale factor for the dilation shown.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 89
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 89
Now,
From the given coordinate plane,
The vertices of Figure DEFG are:
D (0, 0), E (5, 0), F (5, 6), and G (0, 6)
The vertices of Figure D’E’F’G’ are:
D’ (0, 0), E’ (15, 0), G’ (15, 18), and H’ (0, 18)
Now,
We know that,
The “Scale factor” is the ratio of a length in the image to the corresponding length in the preimage
So,
Scale factor = \(\frac{15}{5}\) (or) \(\frac{18}{6}\)
= 3
Hence, from the above,
We can conclude that
The scale factor for the given dilation is: 3

Question 9.
Critique Reasoning For the dilation with center (0, 0) shown on the graph, your friend says the scale factor is \(\frac{5}{2}\). What is the correct scale factor? What mistake did your friend likely make?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 90
Answer:
It is given that
For the dilation with center (0, 0) shown on the graph, your friend says the scale factor is \(\frac{5}{2}\)
Now,
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 90
From the given coordinate plane,
The vertices of ΔABC are:
A (0, 5), B (-5, 0), and C (5, -5)
The vertices of ΔA’B’C’ are:
A’ (0, 2), B’ (-2, 0), C’ (2, -2)
Now,
We know that,
The “Scale factor” is the ratio of a length in the image to the corresponding length in the preimage
So,
Scale factor = \(\frac{2}{5}\) (or) \(\frac{-2}{-5}\)
= \(\frac{2}{5}\)
Hence, from the above,
We can conclude that
The correct scale factor is: \(\frac{2}{5}\)
The mistake done by your friend is:
The consideration of the scale factor as \(\frac{Length of the preimage}{length of the image}\) instead of \(\frac{Length of the image}{Length of the preimage}\)

Question 10.
The smaller figure is the image of dilation of the larger figure. The origin is the center of dilation. Tell whether the dilation is an enlargement or a reduction. Then find the scale factor of the dilation.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 91
Answer:
It is given that
The smaller figure is the image of dilation of the larger figure. The origin is the center of dilation
Now,
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 91
From the given coordinate plane,
The coordinates of each point of the preimage are:
(3, 6), (15, 6), (15, 18), and (3, 18)
The coordinates of each point of the image are:
(1, 2), (5, 2), (5, 6), and (1, 6)
Now,
We know that,
The “Scale factor” is the ratio of a length in the image to the corresponding length in the preimage
So,
Scale factor = \(\frac{1}{3}\) (or) \(\frac{2}{6}\) (or) \(\frac{5}{15}\) (or) \(\frac{6}{18}\)
= \(\frac{1}{3}\)
Now,
Since the scale factor is less than 1, the dilation is a reduction
Hence, from the above,
We can conclude that
The given dilation is a reduction
The scale factor is: \(\frac{1}{3}\)

Question 11.
Higher-Order Thinking Q’R’S’T’ is the image of QRST after a dilation with center at the origin.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 92
Answer:
It is given that
Q’R’S’T’ is the image of QRST after a dilation with center at the origin
Now,
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 92
From the given coordinate plane,
The vertices of the parallelogram QRST are:
Q (4, 4), R (16, 4), S (20, 16), and T (8, 16)
The vertices of the parallelogram Q’R’S’T’ are:
Q’ (1, 1), R’ (4, 1), S’ (5, 4), and T’ (2, 4)

a. Find the scale factor.
Answer:
We know that,
The “Scale factor” is the ratio of a length in the image to the corresponding length in the preimage
So,
Scale factor = \(\frac{4}{1}\) (or) \(\frac{16}{4}\) (or) \(\frac{20}{5}\) (or) \(\frac{8}{2}\)
= 4
Hence, from the above,
We can conclude that the scale factor is: 4

b. Find the area of each parallelogram. What is the relationship between the areas?
Answer:
We know that,
Area of the parallelogram = Base × Height
Now,
the representation of the side lengths of the parallelogram QRST and its dilation Q’R’S’T’ is:

So,
The area of the parallelogram QRST = 12.6 × 12
= 151.2 square units
The area of the parallelogram Q’R’S’T’ = \(\frac{The area of the parallelogram QRST}{4}\)
= 37.8 square units
Hence, from the above,
We can conclude that
The area of the parallelogram QRST is: 151.2 sq. units
The area of the parallelogram Q’R’S’T’ is: 37.8 sq. units
The relationship between the two areas is:
The area of the parallelogram Q’R’S’T’ = \(\frac{The area of the parallelogram QRST}{4}\)

Assessment Practice
Question 12.
Triangle PQR is the image of △JKL after a dilation. Is the dilation an enlargement or a reduction? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 93
A. An enlargement, because the image is larger than the original figure
B. An enlargement, because the image is smaller than the original figure
C. A reduction, because the image is smaller than the original figure
D. A reduction, because the image is larger than the original figure
Answer:
It is given that
Triangle PQR is the image of △JKL after a dilation
Now,
From the given figure,
We can observe that ΔPQR is larger than ΔJKL
So,
We can say that the dilation is an enlargement
Hence, from the above,
We can conclude that option A matches with the given situation

Question 13.
Rectangle QUAD has coordinates Q(0, 0), U(0, 3), A(6, 3), and D(6, 0). Q’U’ A’D’ is the image of QUAD after a dilation with center (0, 0) and a scale factor of 6. What are the coordinates of point D’? Explain.
Answer:
It is given that
Rectangle QUAD has coordinates Q(0, 0), 4(0, 3), A6, 3), and D(6, 0). Q’U’ A’D’ is the image of QUAD after a dilation with center (0, 0) and a scale factor of 6.
So,
With a scale factor of 6,
The vertices of the rectangle QUAD will become:
Q (0 × 6, 0 × 6), U (0 × 6, 3 × 6), A (6 × 6, 3 × 6) and D (6 × 6, 0 × 6)
= Q (0, 0), U (0, 18), A (36, 18), and D (6, 0)
So,
After a dilation,
The vertices of the rectangle QUAD will become the vertices of the rectangle Q’U’A’D’
So,
The vertices of the rectangle Q’U’A’D’ are:
Q’ (0, 0), U’ (0, 18), A’ (36, 18), and D’ (36, 0)
Hence, from the above,
We can conclude that the coordinates of point D’ are: (36, 0)

Lesson 6.7 Understand Similar Figures

Solve & Discuss It!
Andrew draws the two figures shown on a coordinate plane. How are the two figures alike? How are they different? How do you know?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 94
I can… use a sequence of transformations, including dilations, to show that figures are similar.
Answer:
It is given that
Andrew draws the two figures shown on a coordinate plane
Now,
The given figures are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 94
From the above,
We can observe that
ΔABC is the preimage
ΔA’B’C’ is the image
We can also observe that
The image is smaller than the image since the transformation we used when drawing the image is a “Dilation”
Hence,
Since the transformation we used is a “Dilation”,
The two figures are similar in terms of:
a. Shape b. Size c. Orientation d. Angle measures
The two figures are different in terms of:
a. Side lengths

Look for Relationships
Is △ABC a preimage of △A’B’C’? How do you know?
Answer:
The given figures are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 94
From the given figures,
We can clearly observe that the transformation called “Dilation” takes place
Since the dilation takes place,
We can conclude that ΔABC is a preimage of ΔA’B’C’

Focus on math practices
Reasoning How can you use the coordinates of the vertices of the triangles to identify the transformation that maps △ABC to △A’B’C’? Explain.
Answer:
The given figures are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 94
Now,
Fro the given figures,
We know that a transformation called a “Dilation” takes place
So,
We know that,
The “Scale factor” is the ratio of a length in the image to the corresponding length in the preimage
So,
Scale factor = [altex]\frac{The x-coordinate (or) y-coordinate that maps A’ or B’ or C’}{The x-coordinate (or) y-coordinate that maps A or B or C}[/latex}
Hence, from the above,
We can conclude that
By using the “Scale factor”, the coordinates of the vertices of the triangles can be used to identify the transformation that maps △ABC to △A’B’C’

Essential Question
How are similar figures related by a sequence of transformations?
Answer:
Two figures are similar if and only if one figure can be obtained from the other by a single transformation, or a sequence of transformations, including translations, reflections, rotations, and/or dilations. Similarity transformations preserve shape, but not necessarily size, making the figures “similar”

Try It!

Is △ΑΒC similar to △A’ B’ C?
The triangles _________ similar.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 95
Answer:
The given figures are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 95
Now,
If we want to find the 2 triangles are similar or not, find the scale factor and find whether they have the same shape or not
If the scale factor for 2 triangles is the same, then those triangles are similar
Now,
We know that,
The scale factor is defined as the distance from this center point to a point on the preimage and also the distance from the center point to a point on the image
Now,
For AB and A’B’,
Scale factor = \(\frac{27}{12}\)
= \(\frac{9}{4}\)
For BC and B’C’,
Scale factor = \(\frac{27}{12}\)
= \(\frac{9}{4}\)
For AC and A’C’,
Scale factor = \(\frac{18}{8}\)
= \(\frac{9}{4}\)
Since the scale factor is equal for all the corresponding sides
We can conclude that ΔABC is similar to ΔA’B’C’

Convince Me!
What sequence of transformations shows that △ABC is similar to △A’ B’C’?
Answer:
The sequence of Transformations that shows ΔABC is similar to ΔA’B’C’ is:
a. Rotation b. Dilation c. Translation

Try It!

a. Graph the image of JKL after a reflection across the line x = 1 followed by dilation with a scale factor of \(\frac{1}{2}\) and center of dilation point J’.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 96
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 96
From the given coordinate plane,
The vertices of ΔJKL are:
J (-2, -4), K (-4, 0), and L (-2, 1)
The vertices of ΔPQR are:
P (-4, 2), Q (4, 6), and R (6, 2)
Now,
After the reflection of ΔJKL across the line x = 1,
J (-1, 4), K (-3, 0), and L (-1, -1)
So,
With a scale factor of \(\frac{1}{2}\),
The vertices of ΔJKL will become:
J (-1, 4) × \(\frac{1}{2}\), K (-3, 0) × \(\frac{1}{2}\), and L (-1, -1) × \(\frac{1}{2}\)
So,
J’ (-0.5, 2), K’ (-1.5, 0), and L’ (-0.5, -0.5)
Hence,
The representation of the image of JKL after a reflection across the line x = 1 followed by dilation with a scale factor of \(\frac{1}{2}\) and center of dilation point J’ is:

b. Is △JKL similar to △PQR?
Answer:
We know that,
The vertices of ΔJKL are:
J (-2, -4), K (-4, 0), and L (-2, 1)
The vertices of ΔPQR are:
P (-4, 2), Q (4, 6), and R (6, 2)
Now,
Step 1:
Rotate the vertices of ΔJKL 270° about the origin
We know that,
(x, y) before 270° rotation —-> (y, -x) after 270° rotation
So,
The vertices of ΔJKL will be:
J (-4, 2), K (0, 4), and L (1, 2)
Step 2:
Dilate the vertices of ΔJKL we obtained in step 1 by a scale factor of 2
So,
The vertices of ΔJKL will be:
J (-8, 4), K (0, 8), and L (2, 4)
Step 3:
Translate the vertices of ΔJKL we obtained in step 2 by 4 units right and 2 units down
So,
The vertices of ΔJKL will become:
P (-4, 2), Q (4, 6), and R (6, 2)
So,
The representation of the sequence of transformations is:

Hence, from the above,
We can conclude that ΔJKL is similar to ΔPQR

KEY CONCEPT

Two-dimensional figures are similar if there is a sequence of rotations, reflections, translations, and dilations that maps one figure onto the other.

Do You Understand?
Question 1.
Essential Question How are similar figures related by a sequence of transformations?
Answer:
Two figures are similar if and only if one figure can be obtained from the other by a single transformation, or a sequence of transformations, including translations, reflections, rotations, and/or dilations. Similarity transformations preserve the shape, but not necessarily size, making the figures “similar”

Question 2.
Be Precise How do the angle measures and side lengths compare in similar figures?
Answer:
Matching sides of two or more polygons are called corresponding sides, and matching angles are called corresponding angles. If two figures are similar, then the measures of the corresponding angles are equal and the ratios of the lengths of the corresponding sides are proportional.

Question 3.
Generalize Does a given translation, reflection, or rotation, followed by a given dilation, always map a figure to the same image as that same dilation followed by that same translation, reflection, or rotation? Explain.
Answer:
We know that,
The images formed by reflection, translation, and rotation have the same shape and size whereas dilation has the same shape but a different size
In the same way,
The image formed by dilation has the same shape but a different size whereas the image formed by reflection, translation, and rotation has the same shape and size as the image formed in dilation
Hence, from the above,
We can conclude that
The translation, reflection, or rotation, followed by a given dilation, always map a figure to the same image as that same dilation followed by that same translation, reflection, or rotation

Do You Know How?
Question 4.
Is trapezoid ABCD – trapezoid EFGH? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 97
Answer:
The given figures are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 97
From the given figures,
We can observe that
The corresponding angles i.e., the opposite angles are equal
Now,
The ratio of the side lengths of the corresponding figures = \(\frac{32}{16}\) (or) \(\frac{28}{14}\) (or) \(\frac{20}{10}\)
= 2
So,
The ratio of the side lengths of the corresponding figures are the same
Now,
We know that,
Two figures are said to be similar if they are the same shape. In more mathematical language, two figures are similar if their corresponding angles are congruent, and the ratios of the lengths of their corresponding sides are equal. This common ratio is called the scale factor
Hence, from the above,
We can conclude that
Trapezoid ABCD – Trapezoid EFGH

Use the graph for 5 and 6.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 98
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 98
From the given coordinate plane,
The vertices of ΔABC are:
A (-4, -2), B (-1, -2), and C (-3, -3)
The vertices of ΔDEF are:
D (9, -5), E (6, -8), and F (1, -5)

Question 5.
△ABC is dilated by a factor of 2 with a center of dilation at point C, reflected across the x-axis, and translated 3 units up. Graph the resulting similar figure.
Answer:
We know that,
The vertices of ΔABC are:
A (-4, -2), B (-1, -2), and C (-3, -3)
So,
Step 1:
After dilation by a factor of 2:
Multiply all the coordinates of each point by 2
So,
The vertices of ΔABC are:
A (-8, -4), B (-2, -4), and C (-6, -6)
Now,
With a dilation at point C,
Add all the coordinates of each point with -3
So,
The vertices of ΔABC are:
A (-11, -7), B (-5, -7), and C (-9, -9)
Step 2:
When the vertices of ΔABC that we obtained in step 1 reflects across the x-axis,
The vertices of ΔABC will be:
A (-11, 7), B (-5, 7), and C (-9, 9)
Step 3:
When the vertices of ΔABC we obtained in step 2 translated by 3 units up,
Add all the y-coordinates of each point with 3
So,
The vertices of ΔABC will be:
A (-11, 10), B (-5, 10), and C (-9, 12)
Hence,
The representation of all the steps is:

Question 6.
Is △ABC similar to △DEF? Explain.
Answer:
We know that,
The vertices of ΔABC are:
A (-4, -2), B (-1, -2), and C (-3, -3)
The vertices of ΔDEF are:
D (9, -5), E (6, -8), and F (1, -5)
We know that,
Two figures are said to be similar if they are the same shape. In more mathematical language, two figures are similar if their corresponding angles are congruent, and the ratios of the lengths of their corresponding sides are equal
So,
The representation of ΔABC and ΔDEF are:

From the above,
We can observe that the ratio of the corresponding side lengths are not in the same proportion
Hence, from the above,
We can conclude that ΔABC is not similar to ΔDEF

Practice & Problem Solving

Question 7.
Leveled Practice RSTU and VXYZ are quadrilaterals. Given RSTU ~ VXYZ, describe a sequence of transformations that maps RSTU to VXYZ.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 99
• reflection across the ________
• translation ______ unit(s) left and _______ unit(s) up
• dilation with center (0,0) and a scale factor of ________
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 99
From the coordinate plane,
The vertices of the quadrilateral VXYZ are:
V (-2, -1), X (-3, 0), Y (-2, 2), and Z (-1, 0)
The vertices of the quadrilateral RSTU are:
R (3, 0), S (6, 3), T (3, 9), and U (0, 3)
Now,
Step 1:
Reflect the vertices of the quadrilateral VXYZ across the y-axis
So,
The vertices of the quadrilateral VXYZ will be:
V (2, -1), X (3, 0), Y (2, 2), and Z (1, 0)
Step 2:
Dilate the vertices of the quadrilateral VXYZ with a scale factor of 3
So,
Multiply all the coordinates of all the vertices of the quadrilateral VXYZ by 3
So,
The vertices of the quadrilateral VXYZ will be:
V (6, -3), X (9, 0), Y (6, 6), and Z (3, 0)
Step 3:
Translate the vertices of the quadrilateral VXYZ 3 units left and 3 units up
So,
The vertices of the quadrilateral VXYZ will become:
R (3, 0), S (6, 3), T (3, 9), and U (0, 3)
Hence,
The sequence of Transformations that map the quadrilateral VXYZ onto the quadrilateral RSTU is:

Question 8.
Reasoning Is △MNO similar to △PQO? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 100
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 100
From the coordinate plane,
The vertices of ΔMNO are:
M (6, 6 ), N (0, 6), and O (0, 0)
The vertices of ΔPQO are:
P (-12, -9), Q (0, -9), and O (0, 0)
We know that,
Two figures are said to be similar if they are the same shape. In more mathematical language, two figures are similar if their corresponding angles are congruent, and the ratios of the lengths of their corresponding sides are equal
So,
The representation of ΔMNO and ΔPQO are:

From the above,
We can observe that
a. The ratio of the corresponding side lengths are not in the same proportion
b. The angle measures are not the same
Hence, from the above,
We can conclude that ΔMNO is not similar to ΔPQO

Question 9.
△PQR is dilated by a scale factor of 2 with a center of dilation (0, 0) and rotated 180° about the origin. Graph the resulting similar △XYZ.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 101
Answer:
It is given that
△PQR is dilated by a scale factor of 2 with a center of dilation (0, 0) and rotated 180° about the origin.
Now,
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 101
From the given coordinate plane,
The vertices of ΔPQR are:
P (2, 2), Q (4, 2), and R (3, 4)
Now,
Step 1:
Dilation of ΔPQR by a scale factor of 2:
Multiply all the coordinates of each point of ΔPQR by 2
So,
The vertices of ΔPQR will be:
P (4, 4), Q (8, 4), and R (6, 8)
Step 2:
Rotation of 180° counterclockwise about the origin:
We know that,
(x, y) before rotating 180° ——- > (-x, -y) after rotating 180°
So,
The vertices of ΔPQR that we obtained in step 1 will become:
X (-4, -4), Y (-8, -4), and Z (-6, -8)
Hence,
The graph of the resulting ΔXYZ is:

Question 10.
Describe a sequence of transformations that shows that quadrilateral RSTU is similar to quadrilateral VXYZ.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 102
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 102
From the given coordinate plane,
The vertices of the quadrilateral VXYZ are:
V (-5, -5), X (-5, -1), Y (-1, -1), and Z (-1, -5)
The vertices of the quadrilateral RSTU are:
R (-16, -14), S (-16, -6), T (-8, -6), and U (-8, -14)
Now,
Step 1:
Translate the quadrilateral VXYZ 3 units left and 2 units down
So,
The vertices of the quadrilateral VXYZ will be:
V (-8, -7), X (-8, -3), Y (-4, -3), and Z (-4, -7)
Step 2:
Dilate the vertices of the quadrilateral VXYZ we obtained in step 1 by a scale factor of 2
So,
The vertices of the quadrilateral VXYZ will be:
R (-16, -14), S (-16, -6), T (-8, -6), and U (-8, -14)
Hence,
The sequence of Transformations that shows the quadrilateral VXYZ is similar to the quadrilateral RSTU is:

Question 11.
Construct Arguments Is △PQR similar to △XYZ? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 103
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 103
From the given coordinate plane,
The vertices of ΔXYZ are:
X (4, 4), Y (4, 8), and Z (8, 8)
The vertices of ΔPQR are:
P (2, -2), Q (4, -2), and R (4, -4)
Now,
Step 1:
Rotate ΔXYZ 270° about the origin
We know that,
(x, Y) before 270° rotation —— > (y, -x) after 270° rotation
So,
The vertices of ΔXYZ will become:
X ( 4, -4), Y (8, -4), and Z (8, -8)
Step 2:
Dilate ΔXYZ with a scale factor of \(\frac{1}{2}\)
So,
The vertices of ΔXYZ that we obtained in step 1 will become:
P (2, -2), Q (4, -2), and R (4, -4)
So,
After the sequence of Rotation and Dilation of ΔXYZ,
We obtained the vertices of ΔPQR
Hence, from the above,
We can conclude that ΔPQR is similar to ΔXYZ

Question 12.
Higher-Order Thinking Given △JKL ~ △XYZ, find two possible coordinates for missing point Y. For each coordinate chosen, describe a sequence of transformations, including a dilation, that will map △JKL to △XYZ.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 104
Answer:
It is given that
Given △JKL ~ △XYZ
Now,
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 104
From the coordinate plane,
The vertices of ΔJKL are:
J (2, 8), K (6, 2), and L (2, 2)
The vertices of ΔXYZ are:
X (-2, 5), Y (x, y), and Z (-2, 2)
Now,
Step 1:
Reflect ΔJKL across the y-axis
So,
The vertices of ΔJKL will be:
J (-2, 8), K (-6, 2), and L (-2, 2)
Step 2:
Dilate the vertices of ΔJKL that we obtained in step by a scale factor of \(\frac{1}{2}\)
So,
The vertices of ΔJKL will be:
(-1, 4), K (-3, 1), and L (-1, 1)
Step 3:
Translate the vertices of ΔJKL that we obtained in step 2 by 1 unit left and 1 unit up
So,
The vertices of ΔJKL will become:
X (-2, 5), Y (-4, 2), and Z (-2, 2)
Hence, from the above,
We can conclude that the coordinates for the missing point Y are: (-4, 2)

Assessment Practice
Question 13.
Rajesh is making pennants in preparation for a school soccer game. He wants the pennants to be similar triangles. Which of these triangles could he use for the pennants?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 105
A. △QRS and △TVW
B. △QRS and △XYZ
C. △TVW and △JKL
D. △TVW and △XYZ
Answer:
It is given that
Rajesh is making pennants in preparation for a school soccer game. He wants the pennants to be similar triangles.
Now,
If we want to find which of the triangles are similar, find the scale factor and find whether they have the same shape or not
If the scale factor for 2 triangles is the same, then those triangles are similar
Now,
We know that,
The scale factor is defined as the distance from this center point to a point on the preimage and also the distance from the center point to a point on the image
Now,
For ΔQRS and ΔTVW,
Scale factor = \(\frac{3}{1}\) (or) \(\frac{3}{1.5}\)
= 3 (or) 2
For ΔQRS and ΔXYZ,
Scale factor = \(\frac{3}{1.5}\) (or) \(\frac{3}{1.5}\)
= 2
Hence from the above,
We can conclude that ΔQRS and ΔXYZ are similar triangles and he can use these triangles for the pennants

Question 14.
Determine whether the following pairs of triangles are similar or not similar.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 106
Answer:
If we want to find which of the triangles are similar, find the scale factor and find whether they have the same shape or not
If the scale factor for 2 triangles is the same, then those triangles are similar
Now,
We know that,
The scale factor is defined as the distance from this center point to a point on the preimage and also the distance from the center point to a point on the image
Now,
For ΔABC and ΔDEF,
Scale factor = \(\frac{2}{1}\) (or) \(\frac{2}{1}\)
= 2
For ΔABC and ΔLMN,
Scale factor = \(\frac{2}{1.5}\) (or) \(\frac{2}{1}\)
= 1.33 (or) 2
For ΔDEF and ΔLMN,
Scale factor = \(\frac{1}{1}\) (or) \(\frac{1.5}{1}\)
= 1 (or) 1.5
Hence from the above,
We can conclude that ΔABC and ΔDEF are similar triangles

Lesson 6.8 Angles, Lines, and Transversals

Solve & Discuss It!
Draw two parallel lines. Then draw a line that intersects both lines. Which angles have equal measures?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 107
I can… identify and find the measures of angles formed by parallel lines and a transversal.
Answer:
Let a and b be the two parallel lines and the line that is intersecting the parallel lines is a “Transversal”
So,
The representation of the parallel lines along with the transversal is:

Now,
From the above,
The angles that have equal measures are:
Corresponding angles:
∠1 = ∠5, ∠2 = ∠6, ∠3 = ∠7, and ∠4 = ∠8
Alternate Interior angles:
∠4 = ∠6, ∠3 = ∠5
Alternate Exterior angles:
∠1 = ∠7, ∠2 = ∠8
Vertically Opposite Angles:
∠1 = ∠7, ∠2 = ∠8

Use Appropriate Tools
What tools can you use to determine which angles have equal measures?
Answer:
The tools that can be used to determine which angles have equal measures are:
a. Pencil b. Scale c. Protractor d. Setsquare

Focus on math practices
Reasoning What properties or definitions can you use to describe which angles have equal measures?
Answer:
The definitions that you can use to describe which angles have equal measures are:
Corresponding angles:
Corresponding angles are angles that are in the same position relative to lines intersected by a transversal
Alternate Interior angles:
When two parallel lines are crossed by a transversal, the pair of angles formed on the inner side of the parallel lines, but on the opposite sides of the transversal are called alternate interior angles
Alternate Exterior angles:
Alternate exterior angles are the pair of angles that lie on the outer side of the two parallel lines but on either side of the transversal line

Essential Question
What are the relationships among angles that are created when a line intersects two parallel lines?
Answer:
If two parallel lines are cut by a third line, the third line is called the transversal.
So,
The relationships among angles that are created when a line intersects two parallel lines are :
(1) Corresponding angles
(2) Vertically Opposite angles
(3) Alternate interior angles
(4) Alternate exterior angles

Try It!

Which angles are congruent to ∠8?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 108
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 109 Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 109 Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 109
Which angles are supplementary to ∠8?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 109 Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 109 Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 109 Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 109
Answer:
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 108
We know that,
The angle relationships that have equal angle measures are:
a. Corresponding angles b. Vertically opposite angles c. Alternate interior angles d. Alternate exterior angles
We know that,
The angle relationships that have supplementary angle measures are:
a. Adjacent angles
Hence, from the above,
We can conclude that
The angles that are congruent to ∠8 are: ∠4, ∠6 and ∠2
The angles that are supplementary to ∠8 are: ∠7, ∠1, ∠2, and ∠6

Convince Me!
Use what you know about other angle relationships to explain why ∠4 and ∠5 are supplementary angles.
Answer:
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 108
Now,
From the given Transversal,
We can observe that
∠4 and ∠5 are consecutive interior angles
Now,
We know that,
The sum of the consecutive interior angles is always equal to 180°
The angles that have the sum 180° are also called “Supplementary angles”
Hence, from the above,
We can conclude that ∠4 and ∠5 are supplementary angles

Try It!

What are the measures of ∠7 and ∠2? Explain.

Answer:
The given transversal is:

Now,
From the given transversal,
We can observe that
∠4 and 99° are the corresponding angles
∠4 and ∠2 are alternate interior angles
∠5 and ∠7 are vertical angles
∠4 and ∠5 are supplementary angles
So,
Now,
∠4 = 99°
Now,
∠4 + ∠5 = 180°
∠5 = 180° – 99°
∠5 = 81°
Now,
∠2 = 99°
∠7 = 81°
Hence, from the above,
We can conclude that
The values of ∠7 and ∠2 are: 81° and 99° respectively

Try It!

In the figure, a || b. What is the value of x?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 110
Answer:
It is given that a || b
Now,
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 110
From the given transversal,
We can observe that
59° and (x + 12)° are consecutive exterior angles
Now,
We know that,
The sum of the angles of consecutive exterior angles is: 180°
So,
59°+ (x + 12)° = 180°
x + 71° = 180°
x = 180° – 71°
x = 109°
Hence, from the above,
We can conclude that the value of x is: 109°

KEY CONCEPT

If parallel lines are intersected by a transversal, then
• Corresponding angles are congruent.
• Alternate interior angles are congruent.
• Same-side interior angles are supplementary.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 111

Do You Understand?
Question 1.
Essential Question What are the relationships among angles that are created when a line intersects two parallel lines?
Answer:
If two parallel lines are cut by a third line, the third line is called the transversal.
So,
The relationships among angles that are created when a line intersects two parallel lines are :
(1) Corresponding angles
(2) Vertically Opposite angles
(3) Alternate interior angles
(4) Alternate exterior angles

Question 2.
When parallel lines are cut by a transversal, how can you use a translation to describe how angles are related?
Answer:
Let a and b be the parallel lines
Now,
The given transversal is:

Now,
When the parallel lines are cut by a transversal,
The relation between angles is:
Corresponding angles:
∠1 = ∠5, ∠2 = ∠6, ∠3 = ∠7, and ∠4 = ∠8
Alternate Interior angles:
∠4 = ∠6, ∠3 = ∠5
Alternate Exterior angles:
∠1 = ∠7, ∠2 = ∠8
Vertically Opposite Angles:
∠1 = ∠7, ∠2 = ∠8
Consecutive Interior angles:
∠4 + ∠5 = 180°, ∠3 + ∠6 = 180°
Consecutive Exterior angles:
∠1 + ∠8 = 180°, ∠7 + ∠2 = 180°

Question 3.
How many angles are created when two parallel lines are cut by a transversal? How many different angle measures are there?
Answer:
When two parallel lines are cut by a transversal, the number of angles created are: 8
Now,
The different angle measures are:
a. Corresponding angles
b. Alternate Interior angles
c. Alternate Exterior angles
d. Vertical angles
e. Consecutive interior angles
f. Consecutive exterior angles
g. Adjacent angles

Question 4.
Use Structure How can you use angle measures to tell whether two lines are parallel?
Answer:
The ways to prove two lines are parallel using angle measures are:
a. If corresponding angles are congruent.
b. If alternate interior angles are congruent.
c. If consecutive, or same side, interior angles are supplementary.
d. If alternate exterior angles are congruent.

Do You Know How?
In 5-7, use the figure below.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 112

Question 5.
Which angles are congruent to ∠8?
Answer:
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 112
Now,
We know that,
The angle relationships that have equal angle measures are:
a. Corresponding angles b. Vertically opposite angles c. Alternate interior angles d. Alternate exterior angles
Hence, from the above,
We can conclude that
The angles that are congruent to ∠8 are: ∠2, ∠4, and ∠6

Question 6.
If m∠4 = 70°, what is m∠6? Explain.
Answer:
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 112
Now,
From the given transversal,
We can observe that
∠4 and ∠6 are alternate interior angles
We know that,
The alternate interior angles are congruent
Hence, from the above,
We can conclude that
∠4 = ∠6 = 70°

Question 7.
If m∠1 = 95°, write an equation that could be used to find the measure of ∠8. Find m∠8.
Answer:
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 112
Now,
From the given transversal,
We can observe that
∠1 and ∠8 are consecutive exterior angles
Now,
We know that,
The sum of the consecutive exterior angle measures is 180°
So,
∠1 + ∠8 = 180°
∠8 = 180° – ∠1
∠8 = 180° – 95°
∠8 = 85°
Hence, from the above,
We can conclude that the measure of ∠8 is: 85°

Question 8.
What must x equal if line a is parallel to line b?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 113
Answer:
It is given that line a is parallel to line b
Now,
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 113
Now,
From the given transversal,
We can observe that
(2x + 35)° and 103° are the corresponding angles
We know that,
The corresponding angles are congruent
So,
(2x + 35)° = 103°
2x° = 103° – 35°
2x° = 68°
x° = \(\frac{68°}{2}\)
x° = 34°
Hence, from the above,
We can conclude that the value of x is: 34°

Practice & Problem Solving

Question 9.
If p || q, what is the value of u?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 114
Answer:
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 114
From the given transversal,
We can observe that
u and 148° are vertically opposite angles
Now,
We know that.
The vertically opposite angles are always congruent
Hence, from the above,
We can conclude that the value of u is: 148°

Question 10.
Are ∠K and ∠B corresponding angles? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 115
Answer:
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 115
Now,
We know that,
Corresponding angles are angles that are in the same position relative to lines intersected by a transversal
So,
From the given transversal,
We can observe that
∠B is internal and ∠K is external. They are equals if the two intersected lines by the transversal are parallel
Hence, from the above,
We can conclude that
∠K and ∠B are called “Corresponding angles” only when m || n

Question 11.
Streets A and B run parallel to each other. The measure of ∠6 is 155°. What is the measure of ∠4?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 116
Answer:
It is given that
Streets A and B run parallel to each other. The measure of ∠6 is 155°
Now,
The given representation of streets A and B are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 116
Now,
From the given representation,
We can observe that
∠4 and ∠6 are consecutive interior angles
We know that,
The sum of consecutive interior angles is always equal to 180°
So,
∠4 + ∠6 = 180°
∠4 = 180° – ∠6
∠4 = 180° – 155°
∠4 = 25°
Hence, from the above,
We can conclude that the measure of ∠4 is: 25°

Question 12.
Reasoning The figure shows the design of a rectangular windowpane. The four horizontal lines are parallel. The measure of ∠6 is 53°. What is the measure of ∠12? Write and solve an equation to find the answer.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 117
Answer:
It is given that
The figure shows the design of a rectangular windowpane. The four horizontal lines are parallel. The measure of ∠6 is 53°
Now,
The representation of the rectangular windowpane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 117
Now,
From the given representation,
We can observe that
∠6 and ∠12 are consecutive interior angles
We know that,
The sum of consecutive interior angles is: 180°
so,
∠6 + ∠12 = 180°
∠12 = 180° – ∠6
∠12 = 180° – 53°
∠12 = 127°
Hence, from the above,
We can conclude that the angle measure of ∠12 is: 127°

Question 13.
In the figure, m || n. If m∠8 is (4x + 7)° and m∠2 is 107°, what is the value of x? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 118
Answer:
It is given that
m || n and m∠8 is (4x + 7)° and m∠2 is 107°
Now,
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 118
From the given transversal,
We can observe that
∠2 and ∠8 are vertically opposite angles
We know that,
The vertically opposite angles are always congruent
So,
∠2 = ∠8
107° = (4x + 7)°
4x° = 107°- 7°
4x° = 100°
x° = \(\frac{100°}{4}\)
x° = 25°
Hence, from the above,
We can conclude that the value of x is: 25°

Question 14.
For the given figure, can you conclude m || n? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 119
Answer:
The given figure is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 119
Now,
From the given figure,
We can observe that
74° and 74° are alternate interior angles
Now,
We know that,
The Converse of the Alternate Interior Angles Theorem states that if two lines are cut by a transversal and the alternate interior angles are congruent, then the lines are parallel
Hence, from the above,
We can conclude that m || n since the alternate interior angles are congruent

Question 15.
Line m is parallel to line n. Find the value of x and each missing angle measure.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 120
Answer:
It is given that line m is parallel to n
Now,
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 120
From the given transversal,
We can observe that
(2x + 25)° and 86° are vertically opposite angles
We know that,
The vertically opposite angles are always congruent
So,
(2x + 25)° = 86°
2x° = 86°- 25°
2x°= 61°
x° = \(\frac{61°}{2}\)
x° = 30.5°
So,
The value of x is: 30.5°
Now,
We can observe that
∠1 and 86° are supplementary angles
∠1 and ∠3 are vertical angles
∠2 and ∠3 are supplementary angles
(2x + 25)° and ∠6 are supplementary angles
∠6 and ∠4 are vertical angles
∠4 and ∠5 are supplementary angles
So,
∠1 + 86° = 180°
∠1 = 180° – 86°
∠1 = 94°
∠1 = ∠3 = 94°
∠2 + ∠3 = 180°
∠2 = 180° – ∠3
∠2 = 180° – 94°
∠2 = 86°
Now,
(2x + 25)° + ∠6 = 180°
2 (30.5)° + ∠6 = 180° – 25°
∠6 = 155° – 61°
∠6 = 94°
∠ 6 = ∠4 = 94°
∠4 + ∠5 = 180°
∠5 = 180° – ∠4
∠5 = 180° – 94°
∠5 = 96°
Hence, from the above,
We can conclude that
The value of x is: 30.5°
The missing angle measures are:
∠1 = ∠3 = 94°; ∠4 = ∠6 = 94°; ∠2 = 86°; ∠5 = 96°

Question 16.
Higher Order Thinking
a. Find the value of x given that r || s.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 121
m∠1 = (63 – x)°
m∠2 = (72 – 2x)°
Answer:
It is given that r || s
Now,
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 121
From the given transversal,
We can observe that
∠1 and ∠2 are corresponding angles
So,
∠1 = ∠2
So,
(63 – x)° = (72 – 2x)°
2x° – x°= 72° – 63°
x° = 9°
Hence, from the above,
We can conclude that the value of x is: 9°

b. Find m∠1 and m∠2.
Answer:
From part (a),
We can observe that the value of x is: 9°
So,
∠1 = (63 – x)°
∠1 = 63° – 9°
∠1 = 56°
∠2 = (72 – 2x)°
∠2 = 72° – 2 (9)°
∠2 = 72° – 18°
∠2 = 54°
Hence, from the above,
We can conclude that
The values of ∠1 and ∠2 are: 56° and 54° respectively

Question 17.
Find the measures of ∠b and ∠d given that m || n.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 122
Answer:
It is given that m || n
Now,
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 122
From the given transversal,
We can observe that
∠b and 119.3° are supplementary angles
So,
∠b + 119.3° = 180°
∠b = 180° – 119.3°
∠b = 70.7°
Now,
∠d and 136.9° are supplementary angles
So,
∠d + 136.9° = 180°
∠d = 180° – 136.9°
∠d = 43.1°
Hence, from the above,
We can conclude that
The values of ∠b and ∠d are 70.7° and 43.1° respectively

Assessment Practice
Question 18.
In the figure, g || p. Which angles are alternate interior angles? Select all that apply.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 123
☐ ∠q and ∠r
☐ ∠q and ∠t
☐ ∠q and ∠k
☐ ∠r and ∠t
☐ ∠r and ∠k
☐ ∠u and ∠9
Answer:
It is given that g || p
Now,
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 123
From the given transversal,
We can observe that
∠r and ∠k are alternate interior angles
∠q and ∠t are alternate interior angles
Hence, from the above,
We can conclude that
The alternate interior angles are:

Question 19.
In the figure, p || q. On a recent math test, Jacob incorrectly listed the value of w as 101.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 124

PART A
Find the value of w.
Answer:
It is given that p || q
Now,
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 124
From the given transversal,
We can observe that
79° and ∠w are the corresponding angles
Hence, from the above,
We can conclude that the value of ∠w is: 79°

PART B
What mistake did Jacob likely make?
Answer:
We know that,
The corresponding angles are always congruent
Hence,
The mistake that Jacob likely made is:
Jacob considers ∠w  and 101° the corresponding angles

Lesson 6.9 Interior and Exterior Angles of Triangles

Solve & Discuss It!
Nell cuts tile to make a decorative strip for a kitchen backsplash. She must cut the tiles precisely to be congruent triangles. She plans to place the tiles between two pieces of molding, as shown. What is m∠2? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 125
I can… find the interior and exterior angle measures of a triangle.
Answer:
It is given that
Nell cuts tile to make a decorative strip for a kitchen backsplash. She must cut the tiles precisely to be congruent triangles. She plans to place the tiles between two pieces of molding, as shown
Now,
The representation of the decorative strip for a kitchen backsplash is:

Now,
From the given representation,
We can observe that
∠1 of second congruent triangle = ∠1 of the first congruent triangle
∠3 of second congruent triangle = ∠3 of the third congruent triangle
Now,
We know that,
The sum of all the adjacent angles in a transversal is 180°
So,
∠1 + ∠2 + ∠3 = 180°
From the given representation,
∠1 = ∠3 = 65°
So,
∠2 = 180° – (65° + 65°)
∠2 = 180° – 130°
∠2 = 50°
Hence, from the above,
We can conclude that the value of ∠2 is: 50°

Model with Math
How can you use your knowledge of parallel lines and transversals to solve the problem?
Answer:
The representation of the above problem in the form of parallel lines and transversals is:

Now,
From the above figure,
We can observe that
According to the alternate interior angles theorem,
∠1 of second congruent triangle = ∠1 of the first congruent triangle
∠3 of second congruent triangle = ∠3 of the third congruent triangle
Now,
We know that,
The sum of all the adjacent angles in a transversal is 180°

Focus on math practices
Reasoning What assumption(s) did you need to make to find m∠2? Explain why your assumption(s) is reasonable.
Answer:
The assumptions you need to find ∠2 are:
a. ∠1 of the second congruent triangle = ∠1 of the first congruent triangle
b. ∠3 of the second congruent triangle = ∠3 of the third congruent triangle
c. The sum of all the adjacent angles in a transversal is 180°

Essential Question
How are the interior and exterior angles of a triangle related?
Answer:
An exterior angle of a triangle is equal to the sum of the two opposite interior angles. The sum of exterior angle and interior angle is equal to 180 degrees.

Try It!

Find the unknown angle measure in the triangle at the right.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 126
Answer:
The given triangle is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 126
Now,
We know that,
The sum of all the interior angles in a triangle is: 180°
Now,
Let x° be the unknown angle measure
So,
68° + 40° + x° = 180°
x° = 180° – 108°
x° = 72°
Hence, from the above,
We can conclude that the value of the unknown angle measure is: 72°

Convince Me!
Could a triangle have interior angle measures of 23°, 71°, and 96°? Explain.
Answer:
The given interior angle measures of a triangle are 23°, 71°, and 96°
Now,
We know that,
The sum of all the interior angles in a triangle is: 180°
So,
23° + 71° + 96° = 180°
94° + 96° = 180°
190° ≠ 180°
Hence, from the above,
We can conclude that a triangle could not have given interior angle measures

Try It!

What is the measure of the exterior angle shown?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 127
Answer:
The given triangle is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 127
Now,
From the given figure,
We can observe that
(7x – 1)° and (8x + 8)° are interior angle measures
16x° is an exterior angle measure
Now,
We know that,
An exterior angle of a triangle is equal to the sum of the two opposite interior angles. The sum of exterior angle and interior angle is equal to 180 degrees.
So,
16x° = (7x – 1)° + (8x + 8)°
16x° = 15x° + 7°
16x° – 15x° = 7°
x° = 7°
So,
16x° = 16 (7)°
= 112°
Hence, from the above,
We can conclude that the exterior angle measure of the given triangle is: 112°

KEY CONCEPT

The sum of the measures of the interior angles of a triangle is 180°.
m∠1 + m∠2 + m∠3 = 180°
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 128
The measure of an exterior angle of a triangle is equal to the sum of the measures of its remote interior angles.
m∠2 + m∠3 = m∠4

Do You Understand?
Question 1.
Essential Question How are the interior and exterior angles of a triangle related?
Answer:
An exterior angle of a triangle is equal to the sum of the two opposite interior angles. The sum of exterior angle and interior angle is equal to 180 degrees.

Question 2.
Reasoning Maggie draws a triangle with a right angle. The other two angles have equal measures. What are the possible values of the exterior angles for Maggie’s triangle? Explain.
Answer:
It is given that
Maggie draws a triangle with a right angle. The other two angles have equal measures
Now,
We know that,
The sum of the interior angles in a triangle is: 180°
Now,
Let the unknown two angle measures be x°
So,
90° + x° + x° = 180°
2x° = 180° – 90°
2x°= 90°
x° = \(\frac{90°}{2}\)
x° = 45°
So,
The two unknown angle measures are 45° and 45°
Now,
We know that,
An exterior angle of a triangle is equal to the sum of the two opposite interior angles. The sum of exterior angle and interior angle is equal to 180 degrees.
Now,
Let the exterior angle measure be y°
So,
y° = 45° + 45°
y° = 90°
Hence, from the above,
We can conclude that the possible value for the exterior angle measure of Maggie’s triangle is: 90°

Question 3.
Brian draws a triangle with interior angles of 32° and 87°, and one exterior angle of 93°. Draw the triangle. Label all of the interior angles and the exterior angle.
Answer:
It is given that
Brian draws a triangle with interior angles of 32° and 87°, and one exterior angle of 93°
Now,
We know that,
The sum of all the interior angles in a triangle is 180°
Now,
Let the unknown interior angle measure be: x°
So,
x°+ 32° + 87° = 180°
x° = 180° – 119°
x° = 61°
Now,
We know that,
An exterior angle of a triangle is equal to the sum of the two opposite interior angles. The sum of exterior angle and interior angle is equal to 180 degrees.
Now,
Let the unknown exterior angle measure be y°
So,
From the given interior angle measures,
y° = 61° + 32°
So,
In a triangle,
The interior angle measures are 61°, 32°, and 87°
The exterior angle measure is: 93°
Hence,
The representation of the interior angles and the exterior angle of a triangle is:

Do You Know How?
Use the diagram below for 4 and 5. Assume that a || b.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 129

Question 4.
What are the measures of ∠1 and ∠2? Explain.
Answer:
It is given that a || b
Now,
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 129
From the given transversal,
We can observe that
∠1 and 37.3° are vertically opposite angles
So,
∠1 = 37.3°
Now,
We know that,
The sum of all the interior angles in a triangle is 180°
So,
∠1 + 79.4° + ∠2 = 180°
37.3° + 79.4° + ∠2 = 180°
∠2 = 180° – 116.7
∠2 = 63.3°
Hence, from the above,
We can conclude that the measures of ∠1 and ∠2 are 37.3° and 63.3° respectively

Question 5.
What are the measures of ∠3 and ∠4? Explain.
Answer:
It is given that a || b
Now,
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 129
Now,
From the given transversal,
We can observe that
∠3 and ∠4 are the exterior angles
Now,
∠3 = ∠2 + 79.4°
∠3 = 63.3° + 79.4°
∠3 = 132.7°
Now,
∠4 = ∠1 + 79.4°
∠4 = 37.3° + 79.4°
∠4 = 116.7°
Hence, from the above,
We can conclude that the values of ∠3 and ∠4 are: 132.7° and 116.7°

Question 6.
In △ABC, M∠A = x°, m∠B = (2x)°, and m∠C = (6x + 18)°. What is the measure of each angle?
Answer:
It is given that
In ΔABC,
The angle measures of all the interior angles are:
∠A = x°, ∠B = 2x°, and ∠C = (6x + 18)°
Now,
We know that,
The sum of all the interior angles in a triangle is 180°
So,
x° + 2x° + 6x° + 18° = 180°
9x°= 180° – 18°
9x° = 162°
x° = \(\frac{162°}{9}\)
x° = 18°
So,
∠A = 18°
∠B = 2 (18°) = 36°
∠C = (6x + 18)° = 6 (18°) + 18° = 126°
Hence, from the above,
We can conclude that the measure of each angle is: 18°, 36°, and 126°

Practice & Problem Solving

Question 7.
Leveled Practice For the figure shown, find m∠1.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 130
Angle 1 is an _________ angle of the triangle.
m∠1 is equal to the sum of its ___________.
m∠1 = _______° + _______°
m∠1 = _______°
Answer:
The given triangle is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 130
Now,
From the given triangle,
We can observe that
∠1 is the exterior angle
59° and 56° are the interior angle measures
Now,
We know that,
An exterior angle of a triangle is equal to the sum of the two opposite interior angles. The sum of exterior angle and interior angle is equal to 180 degrees.
So,
∠1 = 59° + 56°
∠1 = 115°
Hence, from the above,
We can conclude that the value of ∠1 is: 115°

Question 8.
Find m∠1 and m∠2.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 131
Answer:
The given triangle is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 131
From the given triangle,
We can observe that
There are 2 triangles and ∠1 is the exterior angle for the second triangle
Now,
We know that,
An exterior angle of a triangle is equal to the sum of the two opposite interior angles. The sum of exterior angle and interior angle is equal to 180 degrees.
So,
For the first triangle,
138° = ∠1 + 18°
∠1 = 138° – 18°
∠1 = 120°
For the second triangle,
∠1 = ∠2 + 85°
120° = ∠2 + 85°
∠2 = 120° – 85°
∠2 = 35°
Hence, from the above,
We can conclude that the values of ∠1 and ∠2 are: 120° and 35°

Question 9.
In △ABC, what is m∠c?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 132
Answer:
The given triangle is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 132
Now,
We know that,
The sum of all the interior angles in a triangle is: 180°
So,
x° + (4x)° + (5x – 13)° = 180°
(10x – 13)° = 180°
10x° = 180° + 13°
10x° = 193°
x° = \(\frac{193°}{10}\)
x° = 19.3°
So,
∠C = (5x – 13)°
∠C = 5 (19.3)° – 13°
∠C = 96.5° – 13°
∠C = 83.5°
Hence, from the above,
We can conclude that the value of ∠C is: 83.5°

Question 10.
In the figure, m∠1 = (8x + 7)°, m∠2 = (4x + 14)°, and m∠4 = (13x + 12)°. Your friend incorrectly says that m∠4 = 51°. What is m∠4? What mistake might your friend have made?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 133
Answer:
It is given that
In the given figure, m∠1 = (8x + 7)°, m∠2 = (4x + 14)°, and m∠4 = (13x + 12)°. Your friend incorrectly says that m∠4 = 51°
Now,
The given figure is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 133
From the given figure,
We can observe that
∠1, ∠2, and ∠3 are the interior angles
∠4 is an exterior angle
Now,
We know that,
An exterior angle of a triangle is equal to the sum of the two opposite interior angles. The sum of exterior angle and interior angle is equal to 180 degrees.
The sum of all the interior angles in a triangle is 180°
So,
∠1 + ∠2 + ∠3 = 180°
∠4 = ∠1 + ∠2
So,
(13x + 12)° = (8x + 7)° + (4x + 14)°
13x° + 12° = 12x° + 21°
13x° – 12x° = 21°- 12°
x°= 9°
So,
∠4 = (13x + 12)°
∠4 = 13 (9)° + 12°
∠4 = 117° + 12°
∠4 = 129°
Hence, from the above,
We can conclude that
The value of ∠4 is: 120°
The mistake mightyour friend has made is:
He considered ∠4 as an interior angle and he subtracted the value of ∠4 from 180°

Question 11.
What is m∠1?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 134
Answer:
The given triangle is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 134
Now,
From the given triangle,
We can observe that
∠1 is an exterior angle
26° and 90° are interior angles
Now,
We know that,
An exterior angle of a triangle is equal to the sum of the two opposite interior angles. The sum of exterior angle and interior angle is equal to 180 degrees.
So,
∠1 = 26° + 90°
∠1 = 116°
Hence, from the above,
We can conclude that the value of ∠1 is: 116°

Question 12.
Higher Order Thinking Given that m∠1 = (16x)°, m∠2 = (8x + 21)°, and m∠4 = (25x + 19)°, what is an expression for m∠3? What is m∠3?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 135
Answer:
It is given that
Given that m∠1 = (16x)°, m∠2 = (8x + 21)°, and m∠4 = (25x + 19)°, what is an expression for m∠3
Now,
The given triangle is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 135
From the given figure,
We can observe that
∠1, ∠2, and ∠3 are the interior angles
∠4 is an exterior angle
Now,
We know that,
An exterior angle of a triangle is equal to the sum of the two opposite interior angles. The sum of exterior angle and interior angle is equal to 180 degrees.
The sum of all the interior angles in a triangle is 180°
So,
∠1 + ∠2 + ∠3 = 180°
∠4 = ∠1 + ∠2
So,
(25x + 19)° = (16x)° + (8x + 21)°
25x° + 19° = 24x° + 21°
25x° – 24x° = 21°- 19°
x°= 2°
So,
∠3 = 180° – (16 (2)° + 8 (2)° + 21°)
∠3 = 180° – 69°
∠3 = 111°
Hence, from the above,
We can conclude that
The value of ∠3 is: 111°

Question 13.
A ramp attached to a building is being built to help with deliveries. The angle that the bottom of the ramp makes with the ground is 37.2°. Find the measure of the other acute angle.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 136
Answer:
It is given that
A ramp attached to a building is being built to help with deliveries. The angle that the bottom of the ramp makes with the ground is 37.2°
Now,
The representation of the ramp is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 136
From the above,
We can observe that the ramp is in the form of a right triangle
Now,
We know that,
The sum of all the interior angles in a triangle is: 180°
So,
37.2° + 90° + x° = 180°
127.2° + x° = 180°
x°= 180° – 127.2°
x°= 62.8°
Hence, from the above,
We can conclude that the measure of the other acute angle is: 62.8°

Assessment Practice
Question 14.
The measure of ∠F is 110°. The measure of ∠E is 100°. What is the measure of ∠D?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 137
A. 150°
B. 80°
C. 70°
D. 30°
Answer:
It is given that
The measure of ∠F is 110°. The measure of ∠E is 100°
Now,
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 137
From the given transversal,
We can observe that
∠A and ∠D are the vertical angles
Now,
We know that,
The sum of the adjacent angles is: 180°
So,
∠F + ∠C = 180°
∠B + ∠E = 180°
So,
∠C = 180° – ∠F
∠C = 180°- 110°
∠C = 70°
Now,
∠B = 180° – ∠E
∠B = 180° – 100°
∠B = 80°
Now,
We know that,
The sum of all the interior angles in a triangle is: 180°
So,
∠A + ∠B + ∠C = 180°
70° + 80°+ ∠A = 180°
∠A = 180° – 150°
∠A = 30°
So,
∠D = 30°
Hence, from the above,
We can conclude that the measure of ∠D is: 30°

Question 15.
In the figure, m∠1 = (3x + 12)°, m∠2 = (3x + 18)° and m∠3 = (7x + 10)°. What is m∠3 in degrees?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 138
Answer:
It is given that
m∠1 = (3x + 12)°, m∠2 = (3x + 18)° and m∠3 = (7x + 10)°
Now,
The given triangle is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 138
From the given triangle,
We can observe that
∠1 and ∠2 are the interior angles
∠3 is an exterior angle
Now,
We know that,
An exterior angle of a triangle is equal to the sum of the two opposite interior angles. The sum of exterior angle and interior angle is equal to 180 degrees.
So,
∠3 = ∠1 + ∠2
(7x + 10)° = (3x + 12)° + (3x + 18)°
(7x + 10)° = (6x + 30)°
7x° – 6x° = 30° – 10°
x° = 20°
So,
∠3 = 7 (20)° + 10°
∠3 = 140° + 10°
∠3 = 150°
Hence, from the above,
We can conclude that the measure of ∠3 is 150°

Lesson 6.10 Angle-Angle Triangle Similarity

Explore It!
Justin made two flags for his model sailboat.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 139
I can… use angle measures to determine whether two triangles are similar.

A. Draw and label triangles to represent each flag.
Answer:
It is given that
Justin made two flags for his model sailboat
Hence,
The representation of triangles that represent each flag is:

B. How are the side lengths of the triangles related?
Answer:
The representation of triangles that represent each flag is:

From the given triangles,
We can observe that,
After dilation,
Flag A and Flag B have different side lengths that are divided (or) multiplied by some value of scale factor and the sizes of Flag A and Flag B are different
Hence, from the above,
We can conclude that
After dilation transformation,
The side lengths of Flag A is greater than the side lengths of Flag B

C. How are the angle measurements of the triangles related?
Answer:
The representation of triangles that represent each flag is:

From the given triangles,
We can observe that the apex vertex of Flag A is 46° and the base vertices of Flag B are 67° and 67°
Now,
We know that,
The sum of all the angles in a triangle is 180°
So,
For Flag B,
Let the unknown angle measure be x°
So,
67° + 67° + x° = 180°
x° = 180° – 134°
x° = 46°
So,
For Flag B,
The apex vertex is: 46°
Now,
When we observe two triangles,
The apex vertex of Flag A and Flag B is the same
Hence, from the above,
We can conclude that the corresponding angle measurements for Flag A and Flag B are the same

Focus on math practices
Reasoning Justin makes a third flag that has sides that are shorter than the sides of the small flag. Two of the angles for each flag measure the same. Are the third angles for each flag the same measure? Explain.
Answer:
It is given that
Justin makes a third flag that has sides that are shorter than the sides of the small flag. Two of the angles for each flag measure the same
So,
Two of the angles for each flag are 67° and 67°
Since two angle measures are the same for all the flags, the remaining third angle measure will also be the same
Hence, from the above,
We can conclude that the third angles for each flag have the same measure

Essential Question
How can you use angle measures to determine whether two triangles are similar?
Answer:
The Angle-Angle (AA) Criterion states that if two angles in one triangle are congruent to two angles in another triangle, the two triangles are similar triangles.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 143
∠A ≅ ∠D and B ≅ ∠E,
So,
△ABC – △DEF.

Try It!

Is △ΧΥΖ ~ △LMN?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 140
m∠X = _______
m∠N = ________
The triangles ________ similar.
Answer:
The given triangles are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 140
Now,
For ΔXYZ:
We know that,
The sum of all the angles in a triangle is: 180°
So,
∠X + ∠Y + ∠Z = 180°
∠X = 180° – 92° – 42°
∠X = 180° – 134°
∠X = 46°
For ΔLMN:
We know that,
The sum of all the angles in a triangle is: 180°
So,
∠L + ∠M + ∠N = 180°
∠N = 180° – 92° – 53°
∠N = 180° – 148°
∠N = 32°
Now,
To find whether the given triangles are similar or not,
Find out the angle measures of the corresponding sides
So,
For ΔXYZ and ΔLMN,
∠X = ∠L, ∠Y = ∠M,  ∠Z = ∠N
But,
We can observe that
∠X ≠ ∠L
Hence, from the above,
We can conclude that
Since the angle measure of the corresponding sides are not the same,
ΔXYZ is not similar to ΔLMN

Convince Me!
Use what you know about transformations and parallel lines to explain why the Angle-Angle Criterion is true for all triangles.

Try It!

If QR || YZ, is △XYZ ~ △XRQ? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 141
Answer:
It is given that QR || YZ
Now,
The given figure is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 141
Now,
We know that,
Since the lines are parallel, the angles that corresponding to the sides will also be the same
Hence,
According to the Side – Side criterion,
ΔXYZ is similar to ΔXRQ

Try It!

Find the value of x if the two triangles are similar. Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 142
Answer:
The given triangles are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 142
It is given that two triangles are similar
So,
According to Angle – Angle criterion,
(15x)° = 90°
So,
x° = \(\frac{90°}{15}\)
x° = 6°
Hence, from the above,
We can conclude that the value of x is: 6°

KEY CONCEPT

The Angle-Angle (AA) Criterion states that if two angles in one triangle are congruent to two angles in another triangle, the two triangles are similar triangles.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 143
∠A ≅ ∠D and B ≅ ∠E, so △ABC – △DEF.

Do You Understand?
Question 1.
Essential Question How can you use angle measures to determine whether two triangles are similar?
Answer:
The Angle-Angle (AA) Criterion states that if two angles in one triangle are congruent to two angles in another triangle, the two triangles are similar triangles.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 143
∠A ≅ ∠D and B ≅ ∠E,
So,
△ABC – △DEF.

Question 2.
Construct Arguments Claire says that the AA Criterion should be called the AAA Criterion. Explain why Claire might say this. Do you agree? Explain.
Answer:
It is given that
Claire says that the AA Criterion should be called the AAA Criterion.
Now,
We know that
AA criterion tells us that two triangles are similar if two corresponding angles are equal to each other
Now,
AAA criterion may be reformulated as the AAA (angle-angle-angle) similarity theorem
According to the AAA criterion,
Two triangles have their corresponding angles equal if and only if their corresponding sides are proportional.
So,
From the above two criterions’ statements,
We can observe that the definition of both the criteria are the same
Hence, from the above,
We can conclude that you can agree with Clara

Question 3.
Reasoning Which triangle pairs below are always similar? Explain.
Two right triangles
Two isosceles right triangles
Two equilateral triangles
Answer:
The given pairs of triangles are:
a. Two right triangles
b. Two isosceles right triangles
c. Two equilateral triangles
Now,
We know that,
Two triangles are said to be similar if their corresponding angles are congruent and the corresponding sides are in proportion
Hence, from the above,
We can conclude that
The triangle pairs that are similar are:
a. Two isosceles right triangles
b. Two equilateral triangles

Do You Know How?
Question 4.
Are the two triangles similar? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 144
Answer:
The given triangles are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 144
From the given triangles,
We can observe that the apex angle measure in the first triangle is 44° and the apex angle measure in the second triangle is 46°
Now,
We know that
AA criterion tells us that two triangles are similar if two corresponding angles are equal to each other
So,
44° ≠ 46°
Hence, from the above,
We can conclude that the two triangles are not similar

Question 5.
Is △QRS ~ △QLM? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 145
Answer:
The given triangles are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 145
Now,
From the given triangles,
We can observe that
∠R from ΔQRS = ∠L from ΔQLM
Now,
We know that
AA criterion tells us that two triangles are similar if two corresponding angles are equal to each other
So,
90° = 90°
Hence, from the above,
We can conclude that ΔQRS is similar to ΔQLM

Question 6.
Are the triangles similar? What is the value of x?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 146
Answer:
The given triangles are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 146
Now,
From the given triangles,
We can observe that
The apex angle of the smaller triangle and the apex angle of the larger triangle is the same
Now,
We know that,
AA criterion tells us that two triangles are similar if two corresponding angles are equal to each other
So,
The given two triangles are similar
Now,
According to AAA criterion,
(4x)° and 76° are alternate angles
Now,
We know that,
The alternate angles are always congruent
So,
(4x)° = 76°
x° = \(\frac{76°}{4}\)
x° = 19°
Hence, from the above,
We can conclude that the value of x is: 19°

Practice & Problem Solving

Question 7.
Is △XYZ ~ △XTU?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 147
Answer:
The given triangles are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 147
Now,
We know that,
The sum of all the angles in a triangle is: 180°
So,
In ΔXTU,
103° + ∠T + 48° = 180°
∠T = 180° – 151°
∠T = 29°
Now,
∠T in ΔXTU and ∠Y in ΔXYZ are not the same
Now,
We know that,
AA criterion tells us that two triangles are similar if two corresponding angles are equal to each other
Hence, from the above,
We can conclude that
ΔXTU and ΔXYZ are not similar

Question 8.
For what value of x are △RST and △NSP similar? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 148
Answer:
The given triangles are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 148
Now,
For the given triangles to be equal,
We know that,
AA criterion tells us that two triangles are similar if two corresponding angles are equal to each other
So,
∠T in ΔRST = ∠P in ΔNSP
So,
(x + 19)° = (2x)°
2x° – x°= 19°
x° = 19°
Hence, from the above,
We can conclude that the value of x so that ΔRSt and ΔNSP are similar is: 19°

Question 9.
Is △FGH ~ △JIH? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 149
Answer:
The given triangles are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 149
Now,
We know that,
The sum of all the angles in a triangle is equal to 180°
So,
In ΔJIH,
∠J + ∠I + ∠H = 180°
∠J = 180° – (43° + 35°)
∠J = 180° – 78°
∠J = 102°
So,
From the given triangles,
We can observe that
∠J in ΔJIH and ∠F in ΔFGH are not the same
Now,
We know that,
AA criterion tells us that two triangles are similar if two corresponding angles are equal to each other
Hence, from the above,
We can conclude that ΔRST and ΔJIH are not similar

Question 10.
Are △RST and △NSP similar? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 150
Answer:
The given triangles are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 150
Now,
For the given triangles to be equal,
We know that,
AA criterion tells us that two triangles are similar if two corresponding angles are equal to each other
So,
∠T in ΔRST = ∠P in ΔNSP
So,
(x + 15)° = (2x)°
2x° – x°= 15°
x° = 15°
Hence, from the above,
We can conclude that the value of x so that ΔRSt and ΔNSP are similar is: 15°

Question 11.
Contruct Arguments Describe how to use angle relationships to decide whether any two triangles are similar.
Answer:
According to AA criterion,
If two pairs of corresponding angles in a pair of triangles are congruent, then the triangles are similar. We know this because if two angle pairs are the same, then the third pair must also be equal. When the three angle pairs are all equal, the three pairs of sides must also be in proportion.

Question 12.
Higher Order Thinking Are the triangles shown below similar? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 151
Answer:
The given triangles are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 151
Now,
From the given triangles,
We can observe that
The angle measures for the smaller triangle can be obtained by dividing the angle measures of the larger triangle by 3
But,
We know that,
The angle measures must be equal for both the triangles with the proportionate side lengths
Now,
We know that,
AA criterion tells us that two triangles are similar if two corresponding angles are equal to each other
Hence, from the above,
We can conclude that the given triangles are not similar

Assessment Practice
Question 13.
Which of the following statements are true? Select all that apply.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 152
☐ △XYZ ~ △SQR
☐ △XYZ ~ △QSR
☐ △XYZ ~ △GHI
☐ △GIH ~ △SRQ
☐ △ZXY ~ △GIH
☐ △GHI ~ △SRQ
Answer:
The given triangles are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 152
Now,
From the given triangles,
We can observe that
∠I in ΔGIH or ΔHIG is equal to ∠R in ΔQRS or ΔSRQ
∠G in ΔGIH or ΔGHI is equal to ∠X in ΔXYZ or ΔXZY
Now,
We know that,
AA criterion tells us that two triangles are similar if two corresponding angles are equal to each other
Hence, from the above,
We can conclude that
a. △GIH ~ △SRQ
b. △XYZ ~ △GHI

Question 14.
Is △GHI ~ △QRS? Explain your reasoning.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 153
Answer:
The given triangles are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 153
Now,
From the given triangles,
We can observe that
∠G in ΔGHi and ∠Q in ΔQRS are the same
Now,
We know that,
AA criterion tells us that two triangles are similar if two corresponding angles are equal to each other
Hence, from the above,
We can conclude that ΔGHI and ΔQRS are similar

Topic 6 REVIEW

Topic Essential Question
How can you show that two figures are either congruent or similar to one another?
Answer:
When the two figures are congruent,
a. The shapes and sizes of the two figures are the same
b. The side lengths and the angle measures are the same
c. The orientation is not the same
When the two figures are similar,
a. The shapes and orientations are the same
b. The sizes may are not the same
c. The angle measures are the same but the side lengths are different

Vocabulary Review
Complete each sentence by matching each vocabulary word to its definition. Assume pairs of lines are parallel.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 154
Answer:

Use Vocabulary in Writing
Describe a way to show that △ABC is congruent to △DEF Use vocabulary terms from this Topic in your description.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 155
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 155
From the given coordinate plane,
The vertices of ΔABC are:
A (3, 5), B (6, 2), and C (2, 2)
The vertices of ΔDEF are:
D (-2, -1), E (-5, -4), and F (-1, -4)
Now,
The sequence of transformations to show ΔABC is congruent to ΔDEF is:
Step 1:
Reflect the vertices of ΔABC across the y-axis
Step 2:
Translate the image we obtained in step 1 by 1 unit right and 6 units down so that we can obtain the vertices of ΔDEF
Hence,
The representation of the sequence of transformations to show ΔABC is congruent to ΔDEF is:

Concepts and Skills Review

Lesson 6.1 Analyze Translations

Quick Review
A translation is a transformation that maps each point of the preimage the same distance and in the same direction.

Example
Translate △XYZ 5 units right and 3 units up.
Answer:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 156

Practice
Question 1.
Draw the image after a translation 3 units left and 2 units up.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 157
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 157
Now,
From the given coordinate plane,
The vertices of the preimage are:
(-1, -3), (0.5, 2), (3.5, 2), and (5, -3)
Now,
After the translation of 3 units left and 2 units up,
The vertices of the image will become:
(-1 – 3, -3 + 2), (0.5 – 3, 2 + 2), (3.5 – 3, 2 + 2), and (5 – 3, -3 + 2)
(-4, -1), (-2.5, 4), (0.5, 4), and (2, -1)
Hence,
The representation of the preimage and the image is:

Lesson 6.2 Analyze Reflections

Quick Review
Reflected figures are the same distance from the line of reflection but on opposite sides.

Example
What are the coordinates of the image of △ABC after a reflection across the y-axis?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 158
Answer:
Use the rule (x, y) → (-x, y).
A (-4, 1) → A'(4, 1)
B (-1, 1) → B'(1, 1)
C (-1, 5) → C'(1, 5)

Practice
Use the figure.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 159
Question 1.
What are the coordinates of the image of rectangle WXYZ after a reflection across the X-axis?
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 159
From the given coordinate plane,
The vertices of the rectangle WXYZ are:
W (-4, -2), X (-1, -2), Y (-1, -4), and Z (-4, -4)
Now,
We know that,
If a point reflects across the x-axis,
The x-coordinate will be the same but the y-coordinate will change the sign
So,
(x, y) before reflection —– > (x, -y) after reflection
Hence,
The vertices of the rectangle WXYZ after reflection across the x-axis will become:
W’ (-4, 2), X’ (-1, 2), Y’ (-1, 4), and Z’ (-4, 4)
Hence,
The representation of the rectangle WXYZ (Preimage) and the rectangle W’X’Y’Z’ (Image) is:

Question 2.
What are the coordinates of the image of WXYZ after a reflection across the y-axis?
Answer:
We know that,
The vertices of the rectangle WXYZ are:
W (-4, -2), X (-1, -2), Y (-1, -4), and Z (-4, -4)
Now,
We know that,
If a point reflects across the y-axis,
The y-coordinate will be the same but the x-coordinate will change the sign
So,
(x, y) before reflection —– > (-x, y) after reflection
Hence,
The vertices of the rectangle WXYZ after reflection across the y-axis will become:
W’ (4, -2), X’ (1, -2), Y’ (1, -4), and Z’ (4, -4)
Hence,
The representation of the rectangle WXYZ (Preimage) and the rectangle W’X’Y’Z’ (Image) is:

Lesson 6.3 Analyze Rotations

Quick Review
A rotation turns a figure about a fixed point, called the center of rotation. The angle of rotation is the number of degrees the figure is rotated.

Example
What are the coordinates of the image of △ABC after a 90° rotation about the origin?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 160
Answer:
Use the rule (x, y) → (-y, x).
A(1, 4) → A'(-4, 1)
B(4, 4) → B'(-4, 4)
C(4, 1) → C'(-1, 4)

Practice
Use the figure.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 161
Question 1.
What are the coordinates of the image of quadrilateral STUV after a 180° rotation about the origin?
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 161
Now,
From the given coordinate plane,
The vertices of the quadrilateral STUV are:
S (-4, -2), T (-2, -2), U (-2, -4), and V (-4, -4)
Now,
We know that,
When any point rotates 180° counterclockwise about the origin,
(x, y) before rotating 180° —– > (-x, -y) after rotating 180°
So,
The vertices of the quadrilateral STUV after the rotation of 180° are:
S’ (4, 2), T (2, 2), U (2, 4), and V (4, 4)
Hence,
The representation of the quadrilateral STUV after the rotation of 180° is:

Question 2.
What are the coordinates of the image of quadrilateral STUV after a 270° rotation about the origin?
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 161
Now,
From the given coordinate plane,
The vertices of the quadrilateral STUV are:
S (-4, -2), T (-2, -2), U (-2, -4), and V (-4, -4)
Now,
We know that,
When any point rotates 270° counterclockwise about the origin,
(x, y) before rotating 270° —– > (y, -x) after rotating 270°
So,
The vertices of the quadrilateral STUV after the rotation of 270° are:
S’ (-2, 4), T (-2, 2), U (-4, 2), and V (-4, 4)
Hence,
The representation of the quadrilateral STUV after the rotation of 180° is:

Lesson 6.4 Compose Transformations

Quick Review
To compose a sequence of transformations, perform one transformation, and then use the resulting image to perform the next transformation.

Example
How can you use a sequence of transformations to map Figure A onto Figure B?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 162
Answer:
Translate Figure A 3 units up, and then reflect Figure A across the y-axis.

Practice
Question 1.
Translate rectangle ABCD 5 units down, and then reflect it across the y-axis.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 163
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 163
Now,
From the given coordinate plane,
The vertices of the rectangle ABCD are:
A (-5, 4), B (-1, 4), C (-1, 2), and D (-5, 2)
Now,
The sequence of transformations to draw the image of the rectangle ABCD is:
Step 1:
Translate the rectangle ABCD 5 units down
So,
The vertices of the rectangle ABCD are:
A (-5, 4 – 5), B (-1, 4 – 5), C (-1, 2 – 5), and D (-5, 2 -5)
A (-5, -1), B (-1, -1), C (-1, -3), and D (-5, -3)
Step 2:
Reflect the vertices that we obtained in step 1 across the y-axis
Now,
We know that,
If a point reflects across the y-axis,
The y-coordinate will be the same but the x-coordinate will change the sign
So,
(x, y) before reflection —– > (-x, y) after reflection
So,
The vertices of the rectangle ABCD are:
A (5, -1), B (1, -1), C (1, -3), and D (5, -3)
Hence,
The representation of the sequence of transformations to represent the rectangle ABCD and its image is:

Lesson 6.5 Understand Congruent Figures

Quick Review
Two figures are congruent if a sequence of transformations maps one figure onto the other.

Example
How can you determine if Figure A is congruent to Figure B?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 164
Answer:
Reflect Figure A across the y-axis, and then translate Figure A 6 units up and 1 unit left.

Practice
Question 1.
Is quadrilateral A congruent to quadrilateral B? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 165
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 165
Now,
From the given coordinate plane,
The vertices of quadrilateral A are:
(1, 1), (2, 4), (4, 4), and (5, 1)
The vertices of quadrilateral B are:
(-5, -4), (-4, -1), (-3, -1), and (-2, -4)
Now,
We know that,
The two figures are said to be congruent when
a. The shapes and sizes of the figures must be the same
b. The side lengths of the 2 figures must be the same
c. The angle measures must be the same
So,
The representation of the quadrilateral A and the quadrilateral B is:

Hence, from the above,
We can conclude that quadrilateral A and quadrilateral B are not congruent side their side lengths are not the same

Lesson 6.6 Describe Dilations

Quick Review
A dilation results in an image that is the same shape but not the same size as the preimage.

Example
What dilation maps WXYZ to W’X’Y’Z?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 166
Answer:
A dilation with center at the origin and a scale factor of 2 maps WXYZ to W’X’Y’Z’.

Practice
Use the figure.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 167
Question 1.
What are the coordinates of the image of parallelogram ABCD after a dilation with center (0, 0) and a scale factor of 3?
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 167
Now,
From the given coordinate plane,
The vertices of the parallelogram ABCD are:
A (-4, 1), B (0, 1), C (1, -1), and D (-3, -1)
Now,
After a dilation with center (0, 0) and a scale factor of 3,
The vertices of the parallelogram must be multiplied with 3
So,
A (-4, 1) × 3, B (0, 1) × 3, C (1, -1) × 3, and D (-3, -1) × 3
A’ (-12, 3), B’ (0, 3), C’ (3, -3), and D’ (-9, -3)
Hence, from the above,
We can conclude that the coordinates for the image of the parallelogram ABCD after a dilation with center (0, 0) and a scale factor of 3 is:
A’ (-12, 3), B’ (0, 3), C’ (3, -3), and D’ (-9, -3)

Question 2.
What are the coordinates of the image of parallelogram ABCD after a dilation with center (0, 0) and a scale factor of \(\frac{1}{2}\)?
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 167
Now,
From the given coordinate plane,
The vertices of the parallelogram ABCD are:
A (-4, 1), B (0, 1), C (1, -1), and D (-3, -1)
Now,
After a dilation with center (0, 0) and a scale factor of \(\frac{1}{2}\),
The vertices of the parallelogram must be multiplied with \(\frac{1}{2}\)
So,
A (-4, 1) × \(\frac{1}{2}\), B (0, 1) × \(\frac{1}{2}\), C (1, -1) × \(\frac{1}{2}\), and D (-3, -1) × \(\frac{1}{2}\)
A’ (-2, 0.5), B’ (0, 0.5), C’ (0.5, -0.5), and D’ (-1.5, -0.5)
Hence, from the above,
We can conclude that the coordinates for the image of the parallelogram ABCD after a dilation with center (0, 0) and a scale factor of \(\frac{1}{2}\) is:
A’ (-2, 0.5), B’ (0, 0.5), C’ (0.5, -0.5), and D’ (-1.5, -0.5)

Lesson 6.7 Understand Similar Figures

Quick Review
Two-dimensional figures are similar if there is a sequence of translations, reflections, rotations, and dilations that maps one figure onto the other figure. Similar figures have the same shape, congruent angles, and proportional side lengths.

Example
Is rectangle ABCD ~ rectangle A’B’C’D?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 168
Answer:
All the angles are right angles.
\(\frac{A B}{A^{\prime} B^{\prime}}=\frac{B C}{B^{\prime} C^{\prime}}=\frac{C D}{C^{\prime} D^{\prime}}=\frac{A D}{A^{\prime} D^{\prime}}=\frac{2}{1}\) = 2
The figures have congruent angle measures and proportional side lengths, so they are similar.

Practice
Use the figure.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 169
Question 1.
Is △ABC similar to △A’B’C’ ? Explain.
Answer:
The given coordinate plane is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 169
Now,
From the given coordinate plane,
The vertices of ΔABC are:
A (-4, 1) B (-4, 5), and C (-1, 1)
The vertices of ΔA’B’C’ are:
A’ (8, 2), B’ (8, 10), and C’ (2, 2)
Now,
The sequence of transformations to find whether △ABC is similar to △A’B’C’ or not is:
Step 1:
Reflect the vertices of △ABC across the y-axis
Step 2:
Dilate the vertices of △ABC we obtained in step 1 with center (0, 0) and a scale factor of 2
Hence,
The representation of the sequence of transformations to represent that △ABC is similar to △A’B’C’ is:

Question 2.
What sequence of transformations shows that △ABC is similar to △A’B’C’?
Answer:
The sequence of transformations that shows △ABC is similar to △A’B’C’ is:
Step 1:
Reflect the vertices of △ABC across the y-axis
Step 2:
Dilate the vertices of △ABC we obtained in step 1 with center (0, 0) and a scale factor of 2

Lesson 6.8 Angles, Lines, and Transversals

Quick Review
When parallel lines are intersected by a transversal, corresponding angles are congruent, alternate interior angles are congruent, and same-side interior angles are supplementary.

Example
If m || n, what is the value of x?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 170
Answer:
m∠3 = 45° (5x + 25)°
45+ (5x + 25) = 180 – n
x = 22

Practice
In the figure, a || b. What is the value of x?
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 171
Answer:
It is given that a || b
Now,
The given transversal is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 171
Now,
From the given transversal,
We can observe that
(3x + 9)° and 129° are alternate angles
Now,
We know that,
The alternate angles are always congruent
So,
(3x + 9)° = 129°
3x° = 129° – 9°
3x° = 120°
x° = \(\frac{120°}{3}\)
x°= 40°
Hence, from the above,
We can conclude that the value of x is: 40°

Lesson 6.9 Interior and Exterior Angles of Triangles

Quick Review
The sum of the measures of the interior angles of a triangle is 180°. The measure of an exterior angle of a triangle is equal to the sum of the measures of its remote interior angles.

Example
Find the missing angle measure.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 172
Answer:
x + 40 = 100, so x = 60

Practice
Question 1.
Find the missing angle measure.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 173
Answer:
The given triangle is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 173
Now,
From the given triangle,
The angle measures are 48°, 102°
Let the unknown angle measure be x°
Now,
We know that,
The sum of all the angles in a given triangle is equal to 180°
So,
48°+ 102° + x° = 180°
x° = 180° – 150°
x° = 30°
Hence, from the above,
We can conclude that the missing angle measure is: 30°

Question 2.
Find the value of x.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 174
Answer:
The given triangle is:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 174
Now,
We know that,
The angle measure of an exterior angle is equal to the sum of the remote interior angles that is opposite to the given exterior angle
So,
3x° + 2x° = 115°
5x° = 115°
x° = \(\frac{115°}{3}\)
x° = 23°
Hence, from the above,
We can conclude that the value of x is: 23°

Lesson 6-10 Angle-Angle Triangle Similarity

Quick Review
By the AA Criterion, if two angles in one triangle are congruent to two angles in another triangle, then the triangles are similar.

Example
Is △ABC ~ △DEF? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 175
Answer:
m∠B = 180° – 90° – 37° = 53°
m∠A = m∠D = 90° and m∠B = m∠E = 53°
Because two angles of the triangles are congruent, the triangles are similar by the AA Criterion.

Practice
Question 1.
AB || XY. Is △ABC ~ △XYC? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 176
Answer:
It is given that AB || XY
Now,
The given triangles are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 176
Now,
From the given triangles,
We can observe that
∠A in ΔABC = ∠X in ΔXYC
Now,
We know that,
AA criterion tells us that two triangles are similar if two corresponding angles are equal to each other
Hence, from the above,
We can conclude that ΔABC is similar to ΔXYC

Question 2.
Find the values of x and y given that △ABC is similar to △MNC.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 177
Answer:
It is given that ΔABC is similar to ΔMNC
Now,
The given triangles are:
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 177
Now,
We know that,
The sum of adjacent angles is equal to 180°
So,
4x° + 2x° = 180°
6x° = 180°
x° = \(\frac{180°}{6}\)
x° = 30°
Now,
Since ∠N = 60°,
∠A = 60° (By AA criterion)
Now,
We know that,
The sum of all the interior angles in a triangle is equal to 180°
So,
5y° + 60° + 30° = 180°
5y° = 180° – 90°
5y° = 90°
y° = \(\frac{90°}{5}\)
y° = 18°
Hence, from the above,
We can conclude that the values of x and y are: 30° and 18° respectively

Topic 6 Fluency Practice

Crisscrossed
Solve each equation. Write your answers in the cross-number puzzle below. Each digit, negative sign, and decimal point of your answer goes in its own box.
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 178
I can… solve multistep equations. © 8.EE.C.7b
Envision Math Common Core Grade 8 Answer Key Topic 6 Congruence And Similarity 179

enVision Math Common Core Grade 8 Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations

Go through the enVision Math Common Core Grade 8 Answer Key Topic 5 Analyze and Solve Systems of Linear Equations and finish your homework or assignments.

enVision Math Common Core 8th Grade Answers Key Topic 5 Analyze And Solve Systems Of Linear Equations

Topic Essential Question
What does it mean to solve a system of linear equations?
Answer:
A system of linear equations is just a set of two or more linear equations. In two variables (x and y), the graph of a system of two equations is a pair of lines in the plane

Topic 5 ënVision STEM Project

Did You Know?
After the Boston Tea Party of 1773, many Americans switched to drinking coffee rather than tea because drinking tea was considered unpatriotic.
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 1
Although Brazil is the largest coffee-producing nation in the world, Americans combine to drink 0.2% more coffee each year than Brazilians. The third-ranked nation for total coffee consumption, Germany, consumes approximately 44% as much coffee as either the United States or Brazil.

The United States consumes the most coffee by total weight, but Americans do not drink the most coffee per capita. People in northern European countries like Finland, Norway, and Holland drink more than twice as much coffee as their American counterparts each day.
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 2
In some coffee-producing nations, millions of acres of forest are cleared to make space for coffee farming. Sustainable farms grow coffee plants in natural growing conditions without chemicals and with minimal waste.
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 3
Coffee beans are actually seeds that are harvested from cherries that grow on coffee plants in tropical climates.

Your Task: Daily Grind
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 4
Coffee roasters create coffee blends by mixing specialty coffees with less expensive coffees in order to create unique coffees, reduce costs, and provide customers with consistent flavor. You and your classmates will explore coffee blends while considering the environmental and economic impact of the coffee trade.

Topic 6 GET READY!

Review What You Know!

Vocabulary
Choose the best term from the box to complete each definition.
linear equation
parallel
slope
y-intercept

Question 1.
The value of m in the equation y = mx + b represents the __________ .
Answer:
We know that,
The value of m in the equation
y = mx + b
represents the “Slope”
Hence, from the above,
We can conclude that the best term from the box to complete the given definition is “Slope”

Question 2.
When lines are the same distance apart over their entire lengths, they are _________.
Answer:
We know that,
When lines are the same distance apart over their entire lengths, they are “Parallel”
Hence, from the above,
We can conclude that the best term from the box to complete the given definition is “Parallel”

Question 3.
The _________ is the value b in the equation y = mx + b.
Answer:
We know that,
The “y-intercept” is the value of b in the equation
y = mx + b
Hence, from the above,
We can conclude that the best term from the box to complete the given definition is “y-intercept”

Question 4.
A __________ is a relationship between two variables that gives a straight line when graphed.
Answer:
We know that,
A “Linear relationship” is a relationship between two variables that gives a straight line when graphed
Hence, from the above,
We can conclude that the best term from the box to complete the given definition is “Linear relationship”

Identifying Slope and y-Intercept

Identify the slope and the y-intercept of the equation.
Question 5.
y = 2x – 3
slope = _________
y-intercept = ________
Answer:
The given equation is:
y = 2x – 3
Compare the above equation with
y = mx + b
Where,
m is the slope
b is the y-intercept
Hence, from the above,
We can conclude that
The slope is: 2
The y-intercept is: -3

Question 6.
y =-0.5x + 2.5
slope = _________
y-intercept = ________
Answer:
The given equation is:
y = -0.5x + 2.5
Compare the above equation with
y = mx + b
Where,
m is the slope
b is the y-intercept
Hence, from the above,
We can conclude that
The slope is: -0.5
The y-intercept is: 2.5

Question 7.
y – 1 = -x
slope = _________
y-intercept = ________
Answer:
The given equation is:
y – 1 = -x
Add 1 on both sides
So,
y = -x + 1
Now,
Compare the above equation with
y = mx + b
Where,
m is the slope
b is the y-intercept
Hence, from the above,
We can conclude that
The slope is: -1
The y-intercept is: 1

Graphing Linear Equations

Graph the equation.
Question 8.
y = \(\frac{2}{3}\)x – 2
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 5
Answer:
The given equation is:
y = \(\frac{2}{3}\)x – 2
Hence,
The representation of the given equation in the coordinate plane is:

Question 9.
y = -2x + 1
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 6
Answer:
The given equation is:
y = -2x + 1
Hence,
The representation of the given equation in the coordinate plane is:

Solving Equations for Variables

Solve the equation for y.
Question 10.
y – x = 5
Answer:
The given equation is:
y – x = 5
Add x on both sides
So,
y – x + x = 5 + x
y = x + 5
Hence, from the above,
We can conclude that the value of y is:
y = x + 5

Question 11.
y + 0.2x = -4
Answer:
The given equation is:
y + 0.2x = -4
Subtract with 0.2x on both sides
So,
y + 0.2x – 0.2x = -4 – 0.2x
y = -0.2x – 4
Hence, from the above,
We can conclude that the value of y is:
y = -0.2x – 4

Question 12.
–\(\frac{2}{3}\)x + y = 8
Answer:
The given equation is:
–\(\frac{2}{3}\)x + y = 8
Add with \(\frac{2}{3}\)x on both sides
So,
–\(\frac{2}{3}\)x + \(\frac{2}{3}\)x + y = 8 + \(\frac{2}{3}\)x
y = \(\frac{2}{3}\)x + 8
Hence, from the above,
We can conclude that the value of y is:
y = \(\frac{2}{3}\)x + 8

Language Development

Complete the fishbone map by writing key terms or phrases related to systems of linear equations on each diagonal. Connect supporting ideas on the horizontal lines.
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 7

Topic 5 PICK A PROJECT

PROJECT 5A
What is the most interesting discussion you’ve had with your classmates?
PROJECT: WRITE A SPEECH FOR A DEBATE
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 8

PROJECT 5B
What can you compare with a Venn diagram?
PROJECT: DRAW A VENN DIAGRAM
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 9

PROJECT 5C
What can you do with a smartphone?
PROJECT: CHOOSE A CELL PHONE PLAN
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 10

PROJECT 5D
If you made a stained-glass window, what colors and shapes would you use?
PROJECT: MAKE A MODEL OF A STAINED-GLASS WINDOW
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 11

Lesson 5.1 Estimate Solutions by Inspection

Solve & Discuss It!
Draw three pairs of lines, each showing a different way that two lines can intersect or not intersect. How are these pairs of lines related?
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 12
I can… find the number of solutions of a system of equations by inspecting the equations.
Answer:
The representation of three pairs of lines, each showing a different way that two lines can intersect or not intersect is:

Now,
Parallel lines:
The lines that do not intersect each othse and have the same slope but different y-intercepts
Perpendicular lines:
The lines that intersect each other with the product of the slopes of lines -1 and different y-intercepts
Intersecting lines:
The lines that are neither parallel nor perpendicular are called “Intersecting lines”
Note:
All perpendicular lines should be intersecting lines but all intersecting lines should not be perpendicular lines

Focus on math practices
Look for Relationships Is it possible for any of the pairs of lines drawn to have exactly two points in common? Explain.
Answer:
We know that,
Any pair of lines should intersect at only 1 common point
Hence, from the above,
We can conclude that It is not possible for any of the pairs of lines drawn to have exactly two points in common

Essential Question
How are slopes and y-intercepts related to the number of solutions of a system of linear equations?
Answer:
When slopes and y-intercepts are different, the two lines intersect at one point,
There is only 1 solution.
When slopes are the same, the lines may be either parallel (different y-intercepts)
There are no solutions
If the lines are the same line (Same slopes and same y-intercepts), they intersect at all points,
So, there are infinitely many solutions

Try It!

How many solutions does this system of equations have? Explain.
y = x + 1
y = 2x + 2
The system of equations has ________ solution. The equations have _______ slopes, so the lines intersect at ________ point.
Answer:
The given system of equations are:
y = x + 1 —–(1)
y = 2x + 2 —-(2)
Compare the given system of equations with
y = mx + b
So,
For the first equation,
m = 1, b = 1
For the second equation,
m = 2 and b = 2
Now,
When we observe the slopes and y-intercepts, they are different
We know that,
When slopes and y-intercepts are different, the two lines intersect at one point,
There is only 1 solution.
Hence, from the above,
We can conclude that
The given system of equations have only 1 solution
The equation has 2 slopes
The lines intersect at (-1, 0)

Convince Me!
The equations of a system have the same slopes. What can you determine about the solution of the system of equations?
Answer:
It is given that the equations of a system have the same slopes
Hence,
When slopes are the same and the y-intercepts are different, the lines may be either parallel
So,
There are no solutions
If the lines have the same slopes and the same y-intercepts, they intersect at all points,
So,
There are infinitely many solutions

Try It!

How many solutions does each system of equations have? Explain.
a. y = -3x + 5
y = -3x – 5
Answer:
The given system of equations are:
y = -3x + 5 ——(1)
y = -3x – 5 ——-(2)
Compare the given system of equations with
y = mx + b
So,
For the first equation,
m = -3, b = 5
For the second equation,
m = -3, b = -5
Now,
From the above,
We can observe that there are the same slopes but different y-intercepts
We know that,
When slopes are the same and the y-intercepts are different, the lines may be either parallel and there are no solutions
Hence, from the above,
We can conclude that there are no solutions for the given system of equations

b. y = 3x + 4
5y – 15x – 20 = 0
Answer:
The given system of equations are:
y = 3x + 4
5y – 15x – 20 = 0
Now,
5y = 15x + 20
Divide by 5 into both sides
So,
y = 3x + 4
So,
The given system of equations are:
y = 3x + 4 ——-(1)
y = 3x + 4 ——–(2)
Now,
Compare the given system of equations with
y = mx + b
So,
For the first equation,
m = 3, b = 4
For the second equation,
m = 3, b = 4
Now,
From the above,
We can observe that there are the same slopes and the same y-intercepts
We know that,
When slopes and the y-intercepts are the same,
The lines have infinitely many solutions
Hence, from the above,
We can conclude that there are infinitely many solutions for the given system of equations

KEY CONCEPT

You can inspect the slopes and y-intercepts of the equations in a system of linear equations in order to determine the number of solutions of the system.
One Solution
y = 2x + 4
y = 3x – 1
The slopes are different. The lines intersect at 1 point.

No Solution
y = 3x + 4
y = 3x + 5
The slopes are the same, and the y-intercepts are different. The lines are parallel.

Infinitely Many Solutions
y = 3x + 4
y = 4 + 3x
The slopes are the same, and the y-intercepts are the same. The lines are the same.

Do You Understand?
Question 1.
Essential Question How are slopes and y-intercepts related to the number of solutions of a system of linear equations?
Answer:
When slopes and y-intercepts are different, the two lines intersect at one point,
There is only 1 solution.
When slopes are the same, the lines may be either parallel (different y-intercepts)
There are no solutions
If the lines are the same line (Same slopes and same y-intercepts), they intersect at all points,
So, there are infinitely many solutions

Question 2.
Construct Arguments Macy says that any time the equations in a system have the same y-intercept, the system has infinitely many solutions. Is Macy correct? Explain.
Answer:
It is given that
Macy says that any time the equations in a system have the same y-intercept, the system has infinitely many solutions.
Now,
Consider two equations with the same y-intercept and different slopes.
y = 2x + 3
y = 5x + 3
Compare the above system of equation with
y = mx + b
Hence,
We can say that
This system has only one solution.
Now,
Consider another system of equations with the same y-intercepts and the same slopes
y = x + 7
y = x + 7
Compare the above system of equation with
y = mx + b
Hence,
We can say that
This system has infinitely many solutions.
Hence, from the above,
We can conclude that Macy is not correct

Question 3.
Use Structure How can you determine the number of solutions of a system of linear equations by inspecting its equations?
Answer:
By inspecting the equations, the number of solutions can be determined as mentioned below:
When slopes and y-intercepts are different, the two lines intersect at one point,
There is only 1 solution.
When slopes are the same, the lines may be either parallel (different y-intercepts)
There are no solutions
If the lines are the same line (Same slopes and same y-intercepts), they intersect at all points,
So, there are infinitely many solutions

Do You Know How?
Question 4.
Kyle has x 3-ounce blue marbles and a 5-ounce green marble. Lara has x 5-ounce green marbles and a 3-ounce blue marble. Is it possible for Kyle and Lara to have the same number of green marbles and the same total bag weight, y? Explain.
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 13
Answer:
It is given that
Kyle has x 3-ounce blue marbles and a 5-ounce green marble. Lara has x 5-ounce green marbles and a 3-ounce blue marble.
Now,
The total number of marbles = The total number of green marbles + The total number of blue marbles
So,
For Kyle,
The total number of marbles = x+ 1
For Lara,
The total number of marbles = x + 1
Now,
From the total number of marbles,
We can observe that Kyle and Lara have the same number of marbles
Since Kyla and Lara have the same number of marbles,
The total weight of the marbles will also be the same
Hence, from the above,
We can conclude that
Kyle and Lara have the same number of green marbles and the same total bag weight, y

Question 5.
How many solutions does this system of linear equations have? Explain.
\(\frac{1}{2}\)x = y
y = \(\frac{1}{2}\)x + 3
Answer:
The given system of equations are:
\(\frac{1}{2}\)x = y ——(1)
y = \(\frac{1}{2}\)x + 3 —–(2)
Now,
Comapre the given system of equations with
y = mx + b
So,
For the first equation,
m = \(\frac{1}{2}\), b = 0
For the second equation,
m = \(\frac{1}{2}\), b = 3
We know that,
When slopes are the same, the lines may be either parallel (different y-intercepts)
There are no solutions
Hence, from the above,
We can conclude that the given system of equations have no solutions

Question 6.
How many solutions does this system of linear equations have? Explain.
3y + 6x = 12
8x + 4y = 16
Answer:
The given system of equations are:
3y + 6x = 12
8x + 4y = 16
So,
3y = -6x + 12
Divide by 3 into both sides
So,
y = -2x + 4
So,
4y = -8x + 16
Divide by 4 into both sides
So,
y = -2x + 4
So,
The required system of equations are:
y = -2x + 4 —–(1)
y = -2x + 4 —–(2)
We know that,
If the lines are the same line (Same slopes and same y-intercepts), they intersect at all points,
So, there are infinitely many solutions
Hence, from the above,
We can conclude that the given system of equations have infinitely many solutions

Practice & Problem Solving

Question 7.
Leveled Practice Two rovers are exploring a planet. The system of equations below shows each rover’s elevation, y, at time x. What conclusion can you reach about the system of equations?
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 14
Rover A: y = 1.9x – 8
Rover B: 7y = 13.3x – 56
The slope for the Rover A equation is _________ the slope for the Rover B equation.
The y-intercepts of the equations are ___________.
The system of equations has __________ solution(s).
Answer:
It is given that
Two rovers are exploring a planet. The system of equations below shows each rover’s elevation, y, at time x.
Now,
The given system of equation are:
Rover A: y = 1.9x – 8 ——(1)
Rover B: 7y = 13.3x – 56
Now,
Divide the equation of Rover B with 7
So,
Rover B: y = 1.9x – 8 ——(2)
Now,
When we compare the given system of equations with
y = mx + b
For Rover A,
m = 1.9, b = -8
For Rover B,
m = 1.9, b = -8
We know that,
If the lines are the same line (Same slopes and same y-intercepts), they intersect at all points,
So, there are infinitely many solutions
Hence, from the above,
We can conclude that the given system of equations ahve infinitely many solutions

Question 8.
How many solutions does this system have?
y = x – 3
4x – 10y = 6
Answer:
The given system of equations are:
y = x – 3 ——(1)
4x – 10y = 6
So,
10y = 4x – 6
Divide by 10 into both sides
So,
y = 0.4x – 0.6 ——(2)
Now,
Compare the given system of equations with
y = mx + b
So,
For the first equation,
m = 1, b = -3
For the second equation,
m = 0.4, b = -0.6
We know that,
When slopes and y-intercepts are different, the two lines intersect at one point,
There is only 1 solution.
Hence, from the above,
We can conclude that the given system of equations have only 1 solution

Question 9.
How many solutions does this system have?
x + 3y = 0
12y = -4x
Answer:
The given system of equations are:
x + 3y = 0
12y = -4x
Now,
3y = -x + 0
y = –\(\frac{1}{3}\)x + 0 ——(1)
12y = -4x
y = –\(\frac{4}{12}\)x
y = –\(\frac{1}{3}\)x ——-(2)
Now,
Compare the given system of equations with
y = mx + b
So,
For the first equation,
m = –\(\frac{1}{3}\), b = 0
For the second equation,
m = –\(\frac{1}{3}\), b = 0
We know that,
If the lines are the same line (Same slopes and same y-intercepts), they intersect at all points,
So, there are infinitely many solutions
Hence, from the above,
We can conclude that the given system of equations ahve infinitely many solutions

Question 10.
What can you determine about the solution(s) of this system?
-64x + 96y = 176
56x – 84y = -147
Answer:
The given system of equations are:
-64x + 96y = 176
56x – 84y = -147
So,
96y = 64x + 176
84y = 56x + 147
Now,
Divide by 96 into both sides
y = \(\frac{2}{3}\)x + \(\frac{11}{6}\) ——(1)
Now,
Divide by 84 into both sides
y = \(\frac{2}{3}\)x + \(\frac{7}{4}\) ——-(2)
Now,
Compare the above equations with
y = mx + b
So,
For the first equation,
m = \(\frac{2}{3}\), b = \(\frac{11}{6}\)
For the second equation,
m = \(\frac{2}{3}\), b = \(\frac{7}{4}\)
We know that,
When slopes are the same, the lines may be either parallel (different y-intercepts)
There are no solutions
Hence, from the above,
We can conclude that the given system of equations have no solutions

Question 11.
Determine whether this system of equations has one solution, no solution, or infinitely many solutions.
y = 8x + 2
y = -8x + 2
Answer:
The given system of equations are:
y = 8x + 2 —–(1)
y = -8x + 2 —–(2)
Now,
Compare the given system of equations with
y = mx + b
So,
For the first equation,
m = 8, b = 2
For the second equation,
m = -8, b = 2
We know that,
When slopes and y-intercepts are different or y-intercepts are the same, the two lines intersect at one point,
There is only 1 solution.
Hence, from the above,
We can conclude that the given system of equations have only 1 solution

Question 12.
Construct Arguments Maia says that the two lines in this system of linear equations are parallel. Is she correct? Explain.
2x + y = 14
2y + 4x = 14
Answer:
It is given that
Maia said the below system of linear equations to be paralle
Now,
The given system of equations are:
2x + y = 14
2y + 4x = 14
Now,
y = -2x + 14 —-(1)
2y = -4x + 14
Divide by 2 into both sides
So,
y = -2x + 7 —–(2)
Now,
Compare the given system of equations with
y = mx + b
So,
For the first equation,
m = -2, b = 14
For the second equation,
m = -2, b = 7
We know that,
For the lines to be parallel, the slopes have to be the same and the y-intercepts be different
Hence, from the above,
We can conclude that Maia is correct

Question 13.
Reasoning Describe a situation that can be represented by using this system of equations. Inspect the system to determine the number of solutions and interpret the solution within the context of your situation.
y = 2x + 10
y = x + 15
Answer:
The given system of equations are:
y = 2x + 10 — (1)
y = x + 15 —–(2)
Now,
Compare the above system of equations with
y = mx + b
So,
For the first equation,
m = 2, b = 10
For the second equation,
m = 1, b = 15
We know that,
When the slopes and y-intercepts are different for a system of linear equations,
There is only 1 solution
Hence, from the above,
We can conclude that the given system of equations has only 1 solution

Question 14.
Look for Relationships Does this system have one solution, no solutions, or infinitely many solutions? Write another system of equations with the same number of solutions that uses the first equation only.
12x + 51y = 156
-8x – 34y = -104
Answer:
The given system of equations are:
12x + 51y = 156
-8x – 34y = -104
So,
51y = -12x + 156
Divide by 51 into both sides
So,
y = –\(\frac{4}{17}\)x + \(\frac{52}{17}\) —-(1)
So,
8x + 34y = 104
34y = -8x + 104
Divide by 34 into both sides
So,
y = –\(\frac{4}{17}\)x + \(\frac{52}{17}\) ——-(2)
Now,
Compare the above equations with
y = mx + b
So,
For the first equation,
m = –\(\frac{4}{17}\), b = \(\frac{52}{17}\)
For the second equation,
m = –\(\frac{4}{17}\), b = \(\frac{52}{17}\)
We know that,
When we have the same slopes and the same y-intercepts, the solutions for a system of linear equations are infinite
Now,
Another system of equations with the first equation as one of the equations is:
12x + 51y = 156
48x + 204y = 624
Hence, from the above,
We can conclude that there are infinitely many solutions for the given system of equations

Question 15.
The equations represent the heights, y, of the flowers, in inches, after x days. What does the y-intercept of each equation represent? Will the flowers ever be the same height? Explain.
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 15
Answer:
It is given that
The equations represent the heights, y, of the flowers, in inches, after x days.
Now,
The given system of equations are:
y = 0.7x + 2 —–(1)
y = 0.4x + 2 —–(2)
Now,
Compare the above system of equations with
y = mx + b
So,
For the first equation,
m = 0.7, b = 2
For the second equation,
m = 0.4, b = 2
Now,
We know that
b represents the y-intercept or the initial value
Now,
When we compare the slopes of the equations,
We know that,
The slopes are different
Hence, from the above,
We can conclude that
The y-intercept of each equation represents the initial height of the flowers
The heights of the flowers are not the same

Question 16.
Does this system have one solution, no solution, or an infinite number of solutions?
4x + 3y = 8
8x + y = 2
Answer:
The given system of equations are:
4x + 3y = 8
8x + y = 2
Now,
3y = -4x + 8
Divide by 3 into both sides
So,
y = –\(\frac{4}{3}\)x + \(\frac{8}{3}\) —-(1)
So,
y = -8x + 2 —–(2)
Now,
Compare the above equations with
y = mx + b
So,
For the equation 1,
m = –\(\frac{4}{3}\), b = \(\frac{8}{3}\)
For the equation 2,
m = -8, b = 2
We know that,
When the slopes and y-intercepts of a system of equations are different, the system has only a solution
Hence, from the above,
We can conclude that the given system of equations has only 1 solution

Question 17.
Higher-Order Thinking Under what circumstances does the system of equations Qx + Ry = S and y = Tx + S have infinitely many solutions?
Answer:
The given system of equations are:
Qx + Ry = S
y = Tx + S
So,
Ry = -Qx + S
Divide by R into both sides
So,
y = –\(\frac{Q}{R}\)x + \(\frac{S}{R}\) —–(1)
y = Tx + S —–(2)
Now,
For the given system of equations to have infinitely many solutions,
The slopes must be the same
The y-intercepts must be the same
So,
–\(\frac{Q}{R}\) = T
\(\frac{S}{R}\) = S
Hence, from the above,
We can conclude that the given system of equations will have infinitely many solutions when
–\(\frac{Q}{R}\) = T
\(\frac{S}{R}\) = S

Assessment Practice
Question 18.
By inspecting the equations, what can you determine about the solution(s) of this system?
12y = 9x + 33
20y = 15x + 55
Answer:
The given system of equations are:
12y = 9x + 33 —-(1)
20y = 15x + 55 —-(2)
So,
Divide eq (1) by 12 into both sides
So,
y = \(\frac{3}{4}\)x + \(\frac{11}{4}\) —-(3)
So,
Divide eq (2) by 20 into both sides
So,
y = \(\frac{3}{4}\)x + \(\frac{11}{4}\) —–(4)
Now,
Compare the above equations with
y = mx + b
So,
For the 3rd equation,
m = \(\frac{3}{4}\), b = \(\frac{11}{4}\)
For the 4th equation,
m = \(\frac{3}{4}\), b = \(\frac{11}{4}\)
We know that,
When the slopes and the y-intercepts of a system of equations are different, the system has only 1 solution
Hence, from the above,
We can conclude that the given system of equations has infinitely many solutions

Question 19.
Choose the statement that correctly describes how many solutions there are for this system of equations.
y = \(\frac{2}{3}\)x + 3
y = \(\frac{5}{4}\)x + 3
A. Infinitely many solutions because the slopes are equal and the y-intercepts are equal
B. Exactly one solution because the slopes are equal but the y-intercepts are NOT equal
C. No solution because the slopes are equal and the y-intercepts are NOT equal
D. Exactly one solution because the slopes are NOT equal
Answer:
The given system of equations are:
y = \(\frac{2}{3}\)x + 3 —-(1)
y = \(\frac{5}{4}\)x + 3 —–(2)
Now,
Compare the abovee quations with
y = mx + b
So,
For the first equation,
m = \(\frac{2}{3}\), b = 3
Fpr the second equation,
m = \(\frac{5}{4}\), b = 3
We know that
When the slopes are different and the y-intercepts are the same or different, the system of equations has only 1 solution
Hence, from the above,
We can conclude that option D matches with the given system of equations

Lesson 5.2 Solve Systems by Graphing

Explore It!
Beth and Dante pass by the library as they walk home using separate straight paths.
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 16
I can… find the solution to a system of equations using graphs.

A. Model with Math The point on the graph represents the location of the library. Draw and label lines on the graph to show each possible path to the library.
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 17
Answer:
It is given that
Beth and Dante pass by the library as they walk home using separate straight paths.
Now,
In the graph,
the location of the graph is given
Hence,
The representation of one of the paths of Beth and Dante that are passing through the library in a straight line is:

B. Write a system of equations that represents the paths taken by Beth and Dante.
Answer:
From part (a),
The representation of one of the paths of Beth and Dante that are passing through the library in a straight line is:

So,
From the graph,
The points that are passing through the path of Beth is: (-4, 0), (0, 2)
Now,
Compare the given points with (x1, y1), (x2, y2)
We know that,
Slope (m) = y2 – y1 / x2 – x1
So,
Slope (m) = \(\frac{2 – 0}{0 + 4}\)
= \(\frac{2}{4}\)
= \(\frac{1}{2}\)
We know that,
The form of the linear equation in the slope-intercept form is:
y = mx + b
So,
y = \(\frac{1}{2}\)x + b
2y = x + 2b
Substitute (-4, 0) (or) (0, 2) in the above equation
So,
2b = 4
b = 2
So,
The required equation is:
2y = x + 4
Now,
The points that are passing through the path of Dante is: (-1, -2), (0, 0)
Now,
Compare the given points with (x1, y1), (x2, y2)
We know that,
Slope (m) = y2 – y1 / x2 – x1
So,
Slope (m) = \(\frac{0 + 2}{0 + 1}\)
= \(\frac{2}{1}\)
= 2
We know that,
The form of the linear equation in the slope-intercept form is:
y = mx + b
So,
y = 2x + b
Substitute (-1, -2) (or) (0, 0) in the above equation
So,
b = 0
So,
The required equation is:
y = 2x
Hence, from the above,
We can conclude that
The required system of linear equations are:
2y = x + 4
y = 2x

Focus on math practices
Reasoning What does the point of intersection of the lines represent in the situation?
Answer:
Point of intersection means the point at which two lines intersect. These two lines are represented by the equation
a1x + b1y + c1= 0 and
a2x + b2y + c2 = 0, respectively.
By solving the two equations, we can find the solution for the point of intersection of two lines.

Essential Question
How does the graph of a system of linear equations represent its solution?
Answer:
Each shows two lines that make up a system of equations. If the graphs of the equations intersect, then there is one solution that is true for both equations. If the graphs of the equations do not intersect (for example, if they are parallel), then there are no solutions that are true for both equations.

Try It!

Solve the system by graphing.
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 18
y = 3x + 5
y = 2x + 4
The solution is the point of intersection (______, _______)
Answer:
The given system of equations are:
y = 3x + 5
y = 2x + 4
So,
The representation of the given system of equations in the coordinate plane is:

Hence, from the above,
We can conclude that the solution or the intersection point of the given system of equations is: (-1, 2)

Convince Me!
How does the point of intersection of the graphs represent the solution of a system of linear equations?
Answer:
When you graph an equation, each point (x,y) on the line satisfies the equation. Therefore, when 2 lines intersect, the coordinates of the intersection point satisfy both equations, i.e. the intersection point represents the solution of the set

Try It!

Solve each system by graphing. Describe the solutions.
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 19
a. 5x + y = -3
10x + 2y = -6
Answer:
The given system of equations are:
5x + y = -3
10x + 2y = -6
So,
The representation of the given system of equations in the coordinate plane is:

Hence, from the above,
We can conclude that the given system of equations has infinitely many solutions since both equations are on the same line

b. x + y = 7
2x + 6y = 12
Answer:
The given system of equations are:
x + y = 7
2x + 6y = 12
So,
The representation of the given system of equations in the coordinate plane is:

Hence, from the above,
We can conclude that the given system of equations has only one solution i.e., (7.5, -0.5)

KEY CONCEPT

The solution of a system of linear equations is the point of intersection of the lines defined by the equations.
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 20

Do You Understand?
Question 1.
Essential Question How does the graph of a system of linear equations represent its solution?
Answer:
Each shows two lines that make up a system of equations. If the graphs of the equations intersect, then there is one solution that is true for both equations. If the graphs of the equations do not intersect (for example, if they are parallel), then there are no solutions that are true for both equations.

Question 2.
Reasoning If a system has no solution, what do you know about the lines being graphed?
Answer:
If a system has no solution, it is said to be inconsistent. The graphs of the lines do not intersect, so the graphs are parallel and there is no solution.

Question 3.
Construct Arguments in a system of linear equations, the lines described by each equation have the same slopes. What are the possible solutions to the system? Explain.
Answer:
If the given system of equations has the same slope, then
For the same slope and the same y-intercept – There ate infinitely many solutions
For the same slope and different outputs – There are no solutions

Do You Know How?
In 4-6, graph each system of equations and find the solution.
Question 4.
y = -3x – 5
y = 9x + 7
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 21
Answer:
The given system of equations are:
y = -3x – 5
y = 9x + 7
So,
The representation of the given system of equations in the coordinate plane is:

Hence, from the above,
We can conclude that the solution for the given system of equations is: (-1, -2)

Question 5.
y = 2x – 5
6x + 3y = -15
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 21
Answer:
The given system of equations are:
y = 2x – 5
6x + 3y = -15
So,
The representation of the given system of equations in the coordinate plane is:

Hence, from the above,
We can conclude that the solution for the given system of equations is: (0, -5)

Question 6.
y = -4x + 3
8x + 2y = 8
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 21
Answer:
The given system of equations are:
y = -4x + 3
8x + 2y = 8
So,
The representation of the given system of equations in the coordinate plane is:

Hence, from the above,
We can conclude that there are no solutions for the given system of equations

Practice & Problem Solving

In 7 and 8, graph each system of equations to determine the solution.
Question 7.
x + 4y = 8
3x + 4y = 0
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 21
Answer:
The given system of equations are:
x + 4y = 8
3x + 4y = 0
So,
The representation of the given system of equations in the coordinate plane is:

Hence, from the above,
We can conclude that the solution for the given system of equations is: (-4, 3)

Question 8.
2x – 3y = 6
4x – y = 12
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 21
Answer:
The given system of equations are:
2x – 3y = 6
4x – y = 12
So,
The representation of the given system of equations in the coordinate plane is:

Hence, from the above,
We can conclude that the solution for the given system of equations is: (3, 0)

Question 9.
The total cost, c, of renting a canoe for n hours can be represented by a system of equations.
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 22
a. Write the system of equations that could be used to find the total cost, c, of renting a canoe for n hours.
Answer:
It is given that
The total cost, c, of renting a canoe for n hours can be represented by a system of equations.
Now,
The total cost for renting a canoe (y) = The cost of renting a canoe per hour × The number of hours (n) + Deposit
So,
For River Y,
y = 33n
For River Z,
y = 5n + 13
Hence, from the above,
We can conclude that the system of equations for the total cost of a canoe is:
y = 33n
y = 5n + 13

b. Graph the system of equations.
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 22
Answer:
From part (a),
The system of equations is:
y = 33n
y = 5n + 13
So,
The representation of the given system of equations in the coordinate plane is:

Hence, from the above,
We can conclude that the solution of the given system of equations is: (0.5, 16)

c. When would the total cost for renting a canoe be the same on both rivers? Explain.
Answer:
From the graph that is in part (b),
We can observe that the y-axis passes through 12
Hence,from the above,
We can conclude that the total cost for renting a canoe can be the same on both rivers after 12 hours

Question 10.
Graph the system of equations and determine the solution.
x + 2y = 4
4x + 8y = 64
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 23
Answer:
The given system of equations are:
x + 2y = 4
4x + 8y = 64
So,
The representation of the given system of equations in the coordinate plane is:

Hence, from the above,
We can conclude that there are no solutions for the given system of equations since they are parallel

Question 11.
Graph the system of equations, then estimate the solution.
y = 1.5x + 1
y = -1.5x + 5.5
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 23
Answer:
The given system of equations are:
y = 1.5x + 1
y = -1.5x + 5.5
So,
The representation of the given system of equations in the coordinate plane is:

Hence, from the above,
We can conclude that the estimated solution for the given system of equations is: (1, 3)

In 12 and 13, graph and determine the solution of the system of equations.
Question 12.
-3y = -9x + 3
-6y = -18x – 12
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 24
Answer:
The given system of equations are:
-3y = -9x + 3
-6y = -18x – 12
So,
The representation of the given syetem of equations in the coordinate plane is:

Hence, from the above,
We can conclude that there are no solutions for the given system of equations since they are parallel lines

Question 13.
x + 5y = 0
25y = -5x
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 24
Answer:
The given system of equations are:
x + 5y = 0
25y = -5x
So,
The representation of the given system of equations i the coordinate plane is:

Hence, from the above,
We can conclude that there are infinitely many solutions for the given system of equations since both equations are in the same line

Question 14.
Higher Order Thinking The total cost, c, of making n copies can be represented by a system of equations.
Envision Math Common Core 8th Grade Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 25
a. Estimate how many copies you need to make for the total cost to be the same at both stores.
Answer:
It is given that
The total cost, c, of making n copies can be represented by a system of equations.
We know that,
1 dollar = 0.1 cent
So,
The total cost of making n copies (y) = The number of copies per hour × The number of copies + the cost of machine use
So,
For Store W,
y = 5n —— (1)
For Store Z,
y = 0.20n + 2 —- (2)
Now,
From the given graph,
We can observe that the given system of equations pass through (6, 5)
Hence, from the above,
We can conclude that we have to make 6 copies for the total cost to be the same at both stores

b. If you have to make a small number of copies, which store should you go to? Explain.
Answer:
To make a small number of copies,
We will see which store gives us the less cost for printing the number of copies
So,
From the given information,
We can observe that Store Z gives us the less cost for printing the more number of copies
Hence, from the above,
We can conclude that we will goto Store Z if we have to make small number of copies

Assessment Practice
Question 15.
Consider the following system of equations.
y =-3x + 6
y = 3x – 12
Which statement is true about the system?
A. The graph of the system is a pair of lines that do not intersect.
B. The graph of the system is a pair of lines that intersect at exactly one point.
C. The graph of the system is a pair of lines that intersect at every point.
D. The system has infinitely many solutions.
Answer:
The given system of equations are:
y = -3x + 6
y = 3x – 12
So,
The representation of the given system of equations in the coordinate plane is:

Hence, from the above,
We can conclude that option B matches with the description of the above graph

Question 16.
What is the solution of the system of equations?
Envision Math Common Core 8th Grade Answers Topic 5 Analyze And Solve Systems Of Linear Equations 26
Answer:
The given graph is:
Envision Math Common Core 8th Grade Answers Topic 5 Analyze And Solve Systems Of Linear Equations 26
So,
From the given graph,
We can observe that
The intersection point is: (2.5, -3)
Hence, from the above,
We can conclude that the solution for the given system of equations are: (2.5, 3)

Topic 5 MID-TOPIC CHECKPOINT

Question 1.
Vocabulary How can you determine the number of solutions of a system by looking at the equations? Lesson 5-1
Answer:
A system of two equations can be classified as follows: If the slopes are the same but the y-intercepts are different, the system has no solution. If the slopes are different, the system has one solution. If the slopes are the same and the y-intercepts are the same, the system has infinitely many solutions.

Question 2.
How many solutions does the system of equations have? Explain. Lesson 5-1
2x – 9y = -5
4x – y = 2
Answer:
The given system of equations are:
2x – 9y = -5
4x – y = 2
So,
9y = 2x + 5
y = \(\frac{2}{9}\)x + \(\frac{5}{9}\) —— (1)
So,
y = 4x – 2 —— (2)
Now,
Compare the above equations with
y = mx + b
So,
For the first equation,
m = \(\frac{2}{9}\), b = \(\frac{5}{9}\)
For the second equation,
m = 4, b = -2
We know that,
When the slopes and y-intercepts of a given system of equations are different, the system of equations has only one solution
Hence, from the above,
We can conclude that the given system of equations has only one solution

Question 3.
Graph the system of equations and find the solution. Lesson 5-2
y = 2x – 1
y = \(\frac{1}{2}\)x + 2
Envision Math Common Core 8th Grade Answers Topic 5 Analyze And Solve Systems Of Linear Equations 27
Answer:
The given system of equations are:
y = 2x – 1
y = \(\frac{1}{2}\)x + 2
So,
The representation of the given system of equations in the coordinate plane is:

Hence, from the above,
We can conclude that the solution of the given system of equations is: (2, 3)

Question 4.
One equation in a system is y =-3x + 7. Which equation gives the system no solution? Lesson 5-1
A. y = -3x + 7
B. y = 3x + 5
C. y = -3x + 5
D. y= \(\frac{1}{3}\)x – 7
Answer:
It is given that
One of the equations in a system of equations is:
y = -3x + 7
Now,
For a system of equations to have no solution,
The slopes must be equal but the y-intercepts must be different
So,
With the above description, we have 2 options matched but option A has the same slope and y-intercept as the first equation
Hence, from the above,
We can conclude that option C must be the other equation in the given system of equations

Question 5.
Finn bought 12 movie tickets. Student tickets cost $4, and adult tickets cost $8. Finn spent a total of $60. Write and graph a system of equations to find the number of student and adult tickets Finn bought. Lesson 5-2
Envision Math Common Core 8th Grade Answers Topic 5 Analyze And Solve Systems Of Linear Equations 28
Answer:
It is given that
Finn bought 12 movie tickets. Student tickets cost $4, and adult tickets cost $8. Finn spent a total of $60.
Now,
Let x be the number of student tickets
Let y be the number of adult tickets
So,
x + y = 12 —– (1) [The total number of tickets]
So,
4x + 8y = 60 —– (2) [The total cost of the tickets]
So,
The representation of the above equations in the coordinate plane is:

So,
From the above graph,
The intersection point of the graph is: (9, 3)
Hence, from the above,
We can conclude that
The number of student tickets is: 9
The number of adult tickets is: 3

Question 6.
What value of m gives the system infinitely many solutions? Lesson 5-1
-x + 4y = 32
y = mx + 8
Answer:
The given system of equations are:
-x + 4y = 32
y = mx + 8
So,
4y = x + 32
y = \(\frac{1}{4}\)x + 8 —– (1)
y = mx + 8 ——- (2)
Now,
For the given system of equations to have infinitely many solutions,
The slopes and the y-intercepts of the 2 equations must be equal
So,
m = \(\frac{1}{4}\)
Hence, from the above,
We can conclude that the value of m is: \(\frac{1}{4}\)

Topic 5 MID-TOPIC PERFORMANCE TASK

Perpendicular lines intersect to form right angles. The system of equations below shows perpendicular lines.
Envision Math Common Core 8th Grade Answers Topic 5 Analyze And Solve Systems Of Linear Equations 29

PART A
How many solutions does the system have? Explain.
Answer:
The given graph is:
Envision Math Common Core 8th Grade Answers Topic 5 Analyze And Solve Systems Of Linear Equations 29
From the given graph,
We can observe that there is only 1 intersection point
Hence, from the above,
We can conclude that the given system of equations has only 1 solution

PART B
Identify the slope and y-intercept of each line. What do you notice about the slopes of the lines?
Answer:
From the given graph,
The system of equations is:
y = \(\frac{3}{4}\)x + 1 —— (1)
y = –\(\frac{4}{3}\)x – 2 —— (2)
Now,
Compare the above equations with
y = mx + b
So,
For the first equation,
m = \(\frac{3}{4}\), b = 1
For the second equation,
m = –\(\frac{4}{3}\), b = -2
Now,
From the slopes of the 2 equations,
We can observe that the product of the 2 slopes are equal to -1

PART C
What value of m makes the system show perpendicular lines? Explain.
y = \(\frac{1}{2}\)x + 8
y = mx – 6
Answer:
The given system of equations are:
y = \(\frac{1}{2}\)x + 8 —- (1)
y = mx – 6 —— (2)
Now,
Compare the above equations with
y = mx + b
So,
For the first equation,
m = \(\frac{1}{2}\), b = 8
For the second equation,
m = m, b = -6
We know that,
For the system of equations to be perpendicular,
The product of the slopes must be equal to -1
So,
m1 . m2 = -1
So,
\(\frac{1}{2}\)m = -1
m = -2
Hence, from the above,
We ca conclude that the value of m is: -1

Lesson 5.3 Solve Systems by Substitution

Explain It!
Jackson needs a taxi to take him to a destination that is a little over 4 miles away. He has a graph that shows the rates for two companies. Jackson says that because the slope of the line that represents the rates for On-Time Cabs is less than the slope of the line that represents Speedy Cab Co., the cab ride from On-Time Cabs will cost less.
Envision Math Common Core 8th Grade Answers Topic 5 Analyze And Solve Systems Of Linear Equations 30
I can… solve systems of equations using substitution.

A. Do you agree with Jackson? Explain.
Answer:
It is given that
Jackson needs a taxi to take him to a destination that is a little over 4 miles away. He has a graph that shows the rates for two companies. Jackson says that because the slope of the line that represents the rates for On-Time Cabs is less than the slope of the line that represents Speedy Cab Co., the cab ride from On-Time Cabs will cost less.
Now,
We know that,
For a linear graph,
Quantity 1 (The component of the x-axis) ∝ Quantity 2 (The component of the y-axis)
So,
From the given information,
Slope ∝ Cost
Hence, from the above information,
We can agree with Jackson

B. Which taxi service company should Jackson call? Explain your reasoning.
Answer:
We know that,
The taxi service company must be chosen according to the cost
Hence, from the above,
We can conclude that Jackson should call for an On-Time cabs taxi service since the cost is less

Focus on math practices
Be Precise Can you use the graph to determine the exact number of miles for which the cost of the taxi ride will be the same? Explain.
Answer:
From the given graph,
We can observe that the intersection point is the point where the cost of the taxi ride will be the same
So,
Corresponding to that intersection point, the distance will be calculated for the same cost of the taxi rides
Hence, from the above,
We can conclude that you can use the graph to determine the exact number of miles for which the cost of the taxi ride will be the same

Essential Question When is substitution a useful method for solving systems of equations?
Answer:
The substitution method is most useful for systems of 2 equations in 2 unknowns. The main idea here is that we solve one of the equations for one of the unknowns, and then substitute the result into the other equation.

Try It!

Brandon took a 50-question exam worth a total of 160 points. There were x two-point questions and y five-point questions. How many of each type of question were on the exam?
x + y = 50
2x + 5y = 160
y = _____ – ______
Substitute for y: 2x + 5(_____ – _____) = 160
2x + _____ – ______x = 160
x = ______ two-point questions
Substitute for x: _____ + y = 50
y = _____ five-point questions
Answer:
It is given that
Brandon took a 50-question exam worth a total of 160 points. There were x two-point questions and y five-point questions.
Now,
The given system of equations are:
x + y = 50 —– (1)
2x + 5y = 160 —–(2)
So,
From eq (1),
y = 50 – x
Now,
Substitute y in eq (2)
So,
2x + 5 (50 – x) = 160
2x + 5 (50) – 5x = 160
2x + 250 – 5x = 160
-3x = 160 – 250
-3x = -90
3x = 90
x = \(\frac{90}{3}\)
x = 30
So,
y = 50 – x
y = 50 – 30
y = 20
Hence from the above,
We can conclude that
The number of 2-point questions is: 30
The number of 5-point questions is: 20

Convince Me!
How do you know which equation to choose to solve for one of the variables?
Answer:
The idea of substitution is that if one variable lets you express one variable in terms of the other, you can substitute that expression for the variable in the other equation. That way the second equation only has one variable, and you can solve that

Try It!

Use substitution to solve each system of equations. Explain.
a. y + \(\frac{1}{2}\)x = 3
4y + 2x = -6
Answer:
The given system of equations are:
y + \(\frac{1}{2}\)x = 3 —- (1)
4y + 2x = -6 ——- (2)
So,
From eq (1),
y = 3 – \(\frac{1}{2}\)x
Now,
Substitute y in eq (2)
So,
4 (3 – \(\frac{1}{2}\)x) + 2x = -6
4 (3) – 2x + 2x = -6
12 = -6
Hence, from the above,
We can conclude that there is no solution for the given system of equations

b. y = \(\frac{1}{4}\)x – 2
8y – 2x = -16
Answer:
The given system of equations are:
y = \(\frac{1}{4}\)x – 2 —– (1)
8y – 2x = -16
Now,
Substitute eq (1) in eq (2)
So,
8 (\(\frac{1}{4}\)x – 2) – 2x = -16
2x – 8 (2) – 2x = -16
-16 = -16
16 = 16
Hence, from the above,
We can conclude that there are infinitely many solutions for the given system of equations

KEY CONCEPT

Systems of linear equations can be solved algebraically. When one of the equations can be easily solved for one of the variables, you can use substitution to solve the system efficiently.
STEP 1 Solve one of the equations for one of the variables. Then substitute the expression into the other equation and solve.
STEP 2 Solve for the other variable using either equation.

Do You Understand?
Question 1.
Essential Question when is substitution a useful method for solving systems of equations?
Answer:
The substitution method is most useful for systems of 2 equations in 2 unknowns. The main idea here is that we solve one of the equations for one of the unknowns, and then substitute the result into the other equation.

Question 2.
Generalize when using substitution to solve a system of equations, how can you tell when a system has no solution?
Answer:
When a system has no solution or an infinite number of solutions and we attempt to find a single, unique solution using an algebraic method, such as substitution, the variables will cancel out and we will have an equation consisting of only constants. If the equation is untrue then the system has no solution.

Question 3.
Construct Arguments Kavi solved the system of equations as shown. What mistake did Kavi make? What is the correct solution?
3x + 4y = 33
2x + y = 17
y = 17 – 2x
2x + (17 – 2x) = 17
2x + 17 – 2x = 17
2x – 2x + 17 = 17
17 = 17
Infinitely many solutions
Answer:
The given system of equations are:
3x + 4y = 33 —– (1)
2x + y = 17 —– (2)
From eq (2),
y = 17 – 2x
Now,
Substitute y in eq (1)
So,
3x + 4 (17 – 2x) = 33
3x + 4 (17) – 4 (2x) = 33
3x + 68 – 8x = 33
-5x = 33 – 68
-5x = -35
5x = 35
x = \(\frac{35}{5}\)
x = 7
Hence, from the above,
We can conclude that the mistake did by Kavi is the miswriting of eq (1)

Do You Know How?
In 4-6, solve each system using substitution.
Question 4.
y = \(\frac{1}{2}\)x + 4
x – y = 8
Answer:
The given system of equations are:
y = \(\frac{1}{2}\)x + 4 —– (1)
x – y = 8 —– (2)
Now,
From eq (2),
y = x – 8
Substitute y in eq (1)
So,
x – 8 = \(\frac{1}{2}\)x + 4
x – \(\frac{1}{2}\)x = 4 + 8
\(\frac{1}{2}\)x = 12
x = 12 (2)
x = 24
So,
y = x – 8
y = 24 – 8
y = 16
Hence, from the above,
We can conclude that the solution for the given system of equations is: (24, 16)

Question 5.
3.25x – 1.5y = 1.25
13x – y = 10
Answer:
The given system of equations are:
3.25x – 1.5y = 1.25 —- (1)
13x – y = 10 —-(2)
Now,
From eq (2),
y = 13x – 10
Now,
Substitute y in eq (1)
So,
3.25x – 1.5 (13x – 10) = 1.25
3.25x – 1.5 (13x) + 1.5(10) = 1.25
3.25x – 19.5x + 15 = 1.25
-16.25x = -13.75
16.25x = 13.75
x = 0.84
So,
y = 13x – 10
y = 13 (0.84) – 10
y = 0.92
Hence, from the above,
We can conclude that the solution for the given system of equations is: (0.84, 0.92)

Question 6.
y – 0.8x = 0.5
5y – 2.5 = 4x
Answer:
The given system of equations are:
y – 0.8x = 0.5 —- (1)
5y – 2.5 = 4x —— (2)
Now,
From eq (1),
y = 0.8x + 0.5
Now,
Substitute y in eq (2)
So,
5 (0.8x + 0.5) – 2.5 = 4x
5 (0.8x) + 5 (0.5) – 2.5 = 4x
4x + 2.5 – 2.5 = 4x
4x – 4x + 2.5 = 2.5
2.5 = 2.5
Hence, from the above,
We can conclude that the given system of equations has infinitely many solutions

Practice & Problem Solving

Leveled Practice In 7-9, solve the systems of equations.
Question 7.
Pedro has 276 more hits than Ricky. Use substitution to solve the system of equations to find how many hits Pedro, p, and Ricky, r, have each recorded.
p + r = 2,666
p = r + 276
Envision Math Common Core 8th Grade Answers Topic 5 Analyze And Solve Systems Of Linear Equations 31
It is given that Pedro has 276 more hits than Ricky
Now,
The given system of equations are:
p + r = 2,666
p = r + 276
Now,
STEP 1 Substitute for p to solve for r.
p + r = 2,666
r + 276 + r = 2,666
2r + 276 = 2,666
2r = 2,390
r = 1,195
STEP 2 Substitute for r to solve for p.
p = r + 276
p = 1,195 + 276
p = 1,471
Hence, from the above,
We can conclude that
Pedro has 1,471 hits, and Ricky has 1,195 hits.

Question 8.
2y + 4.4x = -5
y = -2.2x + 4.5
2 (-2.2x + 4.5) + 4.4x = -5
-4.4x + 9 + 4.4x = -5
9 = -5
Hence, from the above,
We can conclude that
The statement is not true. So, there is no solution.

Question 9.
x + 5y = 0
25y = -5x
x = -5y
25y = -5 (-5y)
25y = 25y
Hence, from the above,
We can conclude that
The statement is true. So, there are infinitely many solutions

Question 10.
On a certain hot summer day, 481 people used the public swimming pool. The daily prices are $1.25 for children and $2.25 for adults. The receipts for admission totaled $865.25. How many children and how many adults swam at the public pool that day?
Answer:
It is given that
On a certain hot summer day, 481 people used the public swimming pool. The daily prices are $1.25 for children and $2.25 for adults. The receipts for admission totaled $865.25.
Now,
Let x be the number of children
Let y be the number of adults
So,
x + y = 481 —– (1) [The number of people that used the public swimming pool]
1.25x + 2.25y = 865.25 —– (2) [The receipts for admission]
Now,
From eq (1),
y = 481 – x
Substitute y in eq (2)
So,
1.25x + 2.25 (481 – x) = 865.25
1.25x + 2.25 (481) – 2.25 (x) = 865.25
1.25x + 1,082.25 – 2.25x = 865.25
-x = -217
x = 217
Now,
y = 481 – x
y = 481 – 217
y = 264
Hence,from the above,
We can conclude that
The number of children that swam at the pool is: 217
The number of adults that swam at the pool is: 264

Question 11.
Construct Arguments Tim incorrectly says that the solution of the system of equations is x = -9, y = -4.
6x – 2y = -6
11 = y – 5x
a. What is the correct solution?
Answer:
The given system of equations are:
6x – 2y = -6 —– (1)
11 = y – 5x —— (2)
Now,
From eq (2),
y = 5x + 11
Substitute y in eq (1)
So,
6x – 2 (5x + 11) = -6
6x – 2 (5x) – 2 (11) = -6
6x – 10x – 22 = -6
-4x = 16
x = –\(\frac{16}{4}\)
x = -4
Now,
y = 5x + 11
y = 5 (-4) + 11
y = -20 + 11
y = -9
Hence, from the above,
We can conclude that the correct solution for the given system of equations is: (-4, -9)

b. What error might Tim have made?
Answer:
It is given that
Tim incorrectly says that the solution of the system of equations is x = -9, y = -4.
But, from part (a),
We can observe that x = -4, y = -9
Hence, from the above,
We can conclude that the error that Tim has made is the reversal of the values of x and y in the solution

Question 12.
The number of water bottles, y, filled in x minutes by each of two machines is given by the equations below. Use substitution to determine if there is a point at which the machines will have filled the same number of bottles.
160x + 2y = 50
y + 80x = 50
Answer:
The given system of equations are:
160x + 2y = 50 —— (1)
y + 80x = 50 ——- (2)
Now,
From eq (2),
y = 50 – 80x
Now,
Substitute y in eq (1)
So,
160x + 2 (50 – 80x) = 50
160x + 2 (50) – 2 (80x) = 50
160x + 100 – 160x = 50
100 = 50
Hence, from the above,
We can conclude that at any point, the machines will not have filled the same number of bottles

Question 13.
a. Use substitution to solve the system below.
x = 8y – 4
x + 8y = 6
Answer:
The given system of equations are:
x = 8y – 4 —– (1)
x + 8y = 6 —– (2)
Now,
Substitute eq (1) in eq (2)
So,
8y – 4 + 8y = 6
16y – 4 = 6
16y = 10
y = \(\frac{16}{10}\)
y = 1.6
Now,
x = 8y – 4
x = 8 (1.6) – 4
x = 12.8 – 4
x = 8.8
Hence, from the above,
We can conclude that

b. Reasoning Which expression would be easier to substitute into the other equation in order to solve the problem? Explain.
Answer:
From part (a),
The given system of equations are:
x = 8y – 4 —– (1)
x + 8y = 6 —– (2)
Hence,
From the given equations,
In order to reduce the number of steps,
Eq (1) would be easier to substitute into the other equation in order to solve the problem

Question 14.
The perimeter of a frame is 36 inches. The length is 2 inches greater than the width. What are the dimensions of the frame?
Envision Math Common Core 8th Grade Answers Topic 5 Analyze And Solve Systems Of Linear Equations 32
Answer:
The given frame is:
Envision Math Common Core 8th Grade Answers Topic 5 Analyze And Solve Systems Of Linear Equations 32
From the given frame,
We can observe that it is in the form of a rectangle
Now,
We know that,
The perimeter of a rectangle = 2 (Length + Width)
So,
36 = 2 (W + 2 + W)
36 = 2 (2W + 2)
2W + 2 = \(\frac{36}{2}\)
2W + 2 = 18
2W = 18 – 2
2W = 16
W = \(\frac{16}{2}\)
W = 8
So,
L = W + 2
L = 8 + 2
L = 10
Hence, from the above,
We can conclude that the dimensions of the frame are:
The length of the frame is: 10 inches
The width of the frame is: 8 inches

Question 15.
Higher-Order Thinking The members of the city cultural center have decided to put on a play once a night for a week. Their auditorium holds 500 people. By selling tickets, the members would like to raise $2,050 every night to cover all expenses. Let d represent the number of adult tickets sold at $6.50. Let s represent the number of student tickets sold at $3.50 each.
a. If all 500 seats are filled for a performance, how many of each type of ticket must have been sold for the members to raise exactly $2,050?
Answer:
It is given that
The members of the city cultural center have decided to put on a play once a night for a week. Their auditorium holds 500 people. By selling tickets, the members would like to raise $2,050 every night to cover all expenses. Let d represent the number of adult tickets sold at $6.50. Let s represent the number of student tickets sold at $3.50 each.
Now,
d + s = 500 —– (1) [The total number of people]
6.50d + 3.50s = 2,050 —– (2) [The total expenses]
So,
From eq (1),
d = 500 – s
Now,
Substitute d in eq (1)
So,
6.50 (500 – s) + 3.50s = 2,050
6.50 (500) – 6.50s + 3.50s = 2,050
3,250 – 3s = 2,050
-3s =-1,200
3s = 1,200
s = \(\frac{1,200}{3}\)
s = 400
So,
d = 500 – s
d = 500 – 400
d = 100
Hence, from the above,
We can conclude that
The number of student tickets is: 400
The number of adult tickets is: 100

b. At one performance there were three times as many student tickets sold as adult tickets. If there were 480 tickets sold at that performance, how much below the goal of $2,050 did ticket sales fall?
Answer:
It is given that there were three times as many student tickets as adult tickets
So,
s = 3d
Now,
d + s = 480 —– (1)
So,
d + 3d = 480
4d = 480
d = \(\frac{480}{4}\)
d = 120
So,
s = 3 (120)
s = 360
Now,
The equation for the total expenses is:
6.50d + 3.50s = 6.50 (120) + 3.50 (360)
= 780 + 1,260
= 2,040
Now,
The fall in the ticket sales = $2,050 – $2,040
= $10
Hence, from the above,
We can conclude that there is a fall of $10 to reach the goal of ticket sales of $2,050

Assessment Practice
Question 16.
What statements are true about the solution of the system?
y = 145 – 5x
0.1y + 0.5x = 14.5
☐ There are infinitely many solutions.
☐ (20, 45) is a solution.
☐ (10, 95) is a solution.
☐ There is no solution.
☐ There is more than one solution.
Answer:
Let the given options be named as A, B, C, D, and E
Now,
The given system of equations are:
y = 145 – 5x —- (1)
0.1y + 0.5x = 14.5 —- (2)
Now,
Substitute eq (1) in eq (2)
So,
0.1 (145 – 5x) + 0.5x = 14.5
0.1 (145) – 0.1 (5x) + 0.5x = 14.5
14.5 – 0.5x + 0.5x = 14.5
14.5 – 0.5x = 14.5 – 0.5x
So,
We can say that there are infinitely many solutions for the given system of equations
Hence, from the above,
We can conclude that option A matches with the solution for the given system of equations

Question 17.
At an animal shelter, the number of dog adoptions one weekend was 10 less than 3 times the number of cat adoptions. The number of cat adoptions plus twice the number of dog adoptions was 8. How many cats and how many dogs were adopted that weekend?
Answer:
It is given that
At an animal shelter, the number of dog adoptions one weekend was 10 less than 3 times the number of cat adoptions. The number of cat adoptions plus twice the number of dog adoptions was 8
Now,
Let the cat adoptions be x
Let the dog adoptions be y
So,
y = 3x – 10 —– (1)
x + 2y = 8 ——- (2)
Now,
Substitute eq (1) in eq (2)
So,
x + 2 (3x – 10) = 8
x – 2 (10) + 2 (3x) = 8
x – 20 + 6x = 8
7x = 28
x = \(\frac{28}{4}\)
x = 7
Now,
y = 3x – 10
y = 3 (7) – 10
y = 21 – 10
y = 11
Hence, from the above,
We can conclude that
The number of dogs adopted that weekend is: 11
The number of cats adopted that weekend is: 7

Lesson 5.4 Solve Systems by Elimination

Solve & Discuss It!
A list of expressions is written on the board. How can you make a list of fewer expressions that has the same combined value as those shown on the board? Write the expressions and explain your reasoning.
Envision Math Common Core Grade 8 Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 33
I can… solve systems of equations using elimination.
Answer:

Look for Relationships
How can you use what you know about combining like terms to make your list?
Answer:
Like terms are mathematical terms that have the exact same variables and exponents, but they can have different coefficients. Combining like terms will simplify a math problem and is also the proper form for writing a polynomial. To combine like terms, just add the coefficients of each like term

Focus on math practices
Reasoning Two expressions have a sum of 0. What must be true of the expressions?
Answer:
It is given that two expressions have a sum of 0
Hence,
From the given information,
We can conclude that the expressions are the same but they are of the opposite sign

Essential Question
How are the properties of equality used to solve systems of linear equations?
Answer:
Basically, you can add or subtract anything you wish to both sides of any inequality, and you can multiply or divide, too, by any positive number, to get a simpler inequality, on the way to solving for the variable

Try It!

Use elimination to solve the system of equations.
2r + 3s = 14
6r – 3s = 6
The solution is r = ______, s = _____.
Envision Math Common Core Grade 8 Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 34
Answer:
The given system of equations are:
2r + 3s = 14 —- (1)
6r – s = 6 —– (2)
So,

Hence, from the above,
We can conclude that the solutions for the given system of equations are:
r = \(\frac{25}{4}\) and s = \(\frac{1}{2}\)

Convince Me!
What must be true about a system of equations for a term to be eliminated by adding or subtracting?
Answer:
In the elimination method, you either add or subtract the equations to get an equation in one variable. When the coefficients of one variable are opposites you add the equations to eliminate a variable and when the coefficients of one variable are equal you subtract the equations to eliminate a variable.

Try It!

Use elimination to solve the system of equations.
3x – 5y = -9
x + 2y = 8
Answer:
The given system of equations are:
3x – 5y = -9
x + 2y = 8
So,

Hence, from the above,
We can conclude that the solution for the given system of equations is: (2, 3)

KEY CONCEPT

You can apply the properties of equality to solve systems of linear equations algebraically by eliminating a variable. Elimination is an efficient method when:
• like variable terms have the same or opposite coefficients.
• one or both equations can be multiplied so that like variable terms have the same or opposite coefficients.

Do You Understand?
Question 1.
Essential Question How are the properties of equality used to solve systems of linear equations?
Answer:
Basically, you can add or subtract anything you wish to both sides of any inequality, and you can multiply or divide, too, by any positive number, to get a simpler inequality, on the way to solving for the variable

Question 2.
How is solving a system of equations algebraically similar to solving the system by graphing? How is it different?
Answer:
To solve a system of linear equations graphically we graph both equations in the same coordinate system. The solution to the system will be at the point where the two lines intersect.

Question 3.
Construct Arguments Consider the system of equations. Would you solve this system by substitution or by elimination? Explain.
1\(\frac{3}{4}\)x + y = 2\(\frac{3}{16}\)
\(\frac{1}{4}\)x – y = -1\(\frac{11}{16}\)
Answer:
The given system of equations are:
1\(\frac{3}{4}\)x + y = 2\(\frac{3}{16}\)
\(\frac{1}{4}\)x – y = -1\(\frac{11}{16}\)
Now,
From the above equations,
We can observe that we can eliminate y easily by using the elimination method
Hence, from the above,
We can conclude that we would solve the given system of equations by using the elimination method

Do You Know How?
In 4–6, solve each system of equations by using elimination.
Question 4.
y – x = 28
y + x = 156
Answer:
The given system of equations are:
y – x = 28 —- (1)
y + x = 156 —- (2)
So,

Hence, from the above,
We can conclude that the solution for the given system of equations is: (64, 92)

Question 5.
3c + 6d = 18
6C – 2d = 22
Answer:
The given system of equations are:
3c + 6d = 18 — (1)
6c – 2d = 22 —– (2)
So,

Hence, from the above,
We can conclude that the solution for the given system of equations is: (4, 1)

Question 6.
7x + 14y = 28
5x + 10y = 20
Answer:
The given system of equations are:
7x + 14y = 28 —– (1)
5x + 10y = 20 —– (2)
So,

Hence, from the above,
We can conclude that there are infinitely many solutions for the given system of equations

Practice & Problem Solving

Question 7.
Leveled Practice Solve the system of equations using elimination.
2x – 2y = 4
2x + y = 11
Multiply the first equation by ______.
Envision Math Common Core Grade 8 Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 35
Answer:
The given system of equations are:
2x – 2y = 4 —– (1)
2x + y = 11 —– (2)
So,

Hence, from the above,
We can conclude that the solution for the given system of equations is: (\(\frac{13}{3}\), \(\frac{7}{3}\))

Question 8.
Solve the system of equations using elimination.
2y – 5x = -2
3y + 2x = 35
Answer:
The given system of equations are:
2y – 5x = -2 —- (1)
3y + 2x = 35 —- (2)
So,

Hence, from the above,
We can conclude that the solution for the given system of equations is: (4, 9)

Question 9.
If you add Natalie’s age and Frankie’s age, the result is 44. If you add Frankie’s age to 3 times Natalie’s age, the result is 70. Write and solve a system of equations using elimination to find their ages.
Answer:
It is given that
If you add Natalie’s age and Frankie’s age, the result is 44. If you add Frankie’s age to 3 times Natalie’s age, the result is 70.
Now,
Let Natalie’s age be n
Let Frankie’s age be f
So,
From the given information,
The system of equations that can be formed is:
n + f = 44 —- (1)
f + 3n = 70 —- (2)
Now,
Eq (1) – Eq (2)
So,

Hence, from the above,
We can conclude that
The age of Natalie is: 13 years
The age of Frankie is: 31 years

Question 10.
If possible, use elimination to solve the system of equations.
5x + 10y = 7
4x + 8y = 3
Answer:
The given system of equations are:
5x + 10y = 7 —- (1)
4x + 8y = 3 —— (2)
So,

Hence, from the above,
We can conclude that the given system of equations has no solution

Question 11.
At a basketball game, a team made 56 successful shots. They were a combination of 1- and 2-point shots. The team scored 94 points in all. Use elimination to solve the system of equations to find the number of each type of shot.
x + y = 56
x + 2y = 94
Answer:
It is given that
At a basketball game, a team made 56 successful shots. They were a combination of 1- and 2-point shots. The team scored 94 points in all
Now,
The given system of equations that represent the given situation is:
x + y = 56 —- (1)
x + 2y = 94 —- (2)
Now,
Eq (1) – Eq (2)
So,

Hence, from the above,
We can conclude that
The number of 1-point shots is: 18
The number of 2-point shots is: 38

Question 12.
Two trains, Train A and Train B, weigh a total of 312 tons. Train A is heavier than Train B. The difference in their weights is 170 tons. Use elimination to solve the system of equations to find the weight of each train.
a + b = 312
a – b= 170
Envision Math Common Core Grade 8 Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 36
Answer:
It is given that
Two trains, Train A and Train B weigh a total of 312 tons. Train A is heavier than Train B. The difference in their weights is 170 tons.
Now,
The system of equations given that describes the given situation is:
a + b = 312 —– (1)
a – b = 170 —— (2)
Now,
Eq (1) – Eq (2)
So,

Hence, from the above,
We can conclude that
The weight of Train A is: 241 tons
The weight of Train B is: 71 tons

Question 13.
A deli offers two platters of sandwiches. Platter A has 2 roast beef sandwiches and 3 turkey sandwiches. Platter B has 3 roast beef sandwiches and 2 turkey sandwiches.
Envision Math Common Core Grade 8 Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 37
a. Model with Math Write a system of equations to represent the situation.
Answer:
It is given that
A deli offers two platters of sandwiches. Platter A has 2 roast beef sandwiches and 3 turkey sandwiches. Platter B has 3 roast beef sandwiches and 2 turkey sandwiches.
Now,
Let a piece of roast beef sandwich be r
Let a piece of turkey beef sandwich be t
So,
In plate A,
The number of sandwiches is: 2r + 3t
In plate B,
The number of sandwiches is: 3r + 2t
Now,
From the above figure,
The total cost of plates A and B are:
2r + 3t = 31
3r + 2t = 29
Hence, from the above,
We can conclude that the system of equations that represent the given situation is:
2r + 3t = 31
3r + 2t = 29

b. What is the cost of each sandwich?
Answer:
From part (a),
The system of equations are:
2r + 3t = 31 —– (1)
3r + 2t = 29 —– (2)
So,

Hence, from the above,
We can conclude that
The cost of each roast beef sandwich is: $5
The cost of each turkey beef sandwich is: $7

Question 14.
Consider the system of equations.
x – 3.1y = 11.5
-x + 3.5y = -13.5
a. Solve the system by elimination.
Answer:
The given system of equations are:
x – 3.1y = 11.5 —- (1)
-x + 3.5y = -13.5 —— (2)
Now,
Eq (1) – Eq (2)
So,

Hence, from the above,
We can conclude that the solution for the given system of equations is: (-4, -5)

b. If you solved this equation by substitution instead, what would the solution be? Explain.
Answer:
By using the substitution method,
The solution for the given system of equations is:

Hence, from the above,
We can conclude that the solution for the substitution method is the same as the solution for the elimination method

Question 15.
Higher-Order Thinking Determine the number of solutions for this system of equations by inspection only. Explain.
3x + 4y = 17
21x + 28y = 109
Answer:
The given system of equations are:
3x + 4y = 17 —– (1)
21x + 28y = 109 —— (2)
So,

Hence, from the above,
We can conclude that there is no solution for the given system of equations

Assessment Practice
Question 16.
Four times a number r plus half a number s equals 12. Twice the number r plus one fourth of the number s equals 8. What are the two numbers?
Answer:
It is given that
Four times a number r plus half a number s equals 12. Twice the number r plus one-fourth of the number s equals 8.
So,
4r + \(\frac{1}{2}\)s = 12 —- (1)
2r + \(\frac{1}{4}\)s = 8 —- (2)
So,

Hence, from the above,
We can conclude that the values for the 2 numbers are not possible

Question 17.
Solve the system of equations.
3m + 3n = 36
8m – 5n = 31
Answer:
The given system of equations are:
3m + 3n = 36 —- (1)
8m – 5n = 31 —– (2)
So,

Hence, from the above,
We can conclude that the solution for the given system of equations is: (7, 5)

3-ACT MATH

3-Act Mathematical Modeling: Ups and Downs
Envision Math Common Core Grade 8 Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 38

ACT 1
Question 1.
After watching the video, what is the first question that comes to mind?
Answer:

Envision Math Common Core Grade 8 Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 39
Question 2.
Write the Main Question you will answer.
Answer:

Question 3.
Make a prediction to answer this Main Question.
The person who wins took the ______.
Answer:

Question 4.
Construct Arguments Explain how you arrived at your prediction.
Answer:

ACT 2
Question 5.
What information in this situation would be helpful to know? How would you use that information?
Answer:

Question 6.
Use Appropriate Tools What tools can you use to solve the problem? Explain how you would use them strategically.
Answer:

Question 7.
Model with Math Represent the situation using mathematics. Use your representation to answer the Main Question.
Answer:

Question 8.
What is your answer to the Main Question? Does it differ from your prediction? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 40
Answer:

ACT 3
Question 9.
Write the answer you saw in the video.
Envision Math Common Core Grade 8 Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 41
Answer:

Question 10.
Reasoning Does your answer match the answer in the video? If not, what are some reasons that would explain the difference?
Answer:

Question 11.
Make Sense and Persevere Would you change your model now that you know the answer? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 5 Analyze And Solve Systems Of Linear Equations 42
Answer:

ACT 3 Extension
Reflect
Question 12.
Model with Math Explain how you used a mathematical model to represent the situation. How did the model help you answer the Main Question?
Envision Math Common Core Grade 8 Answers Topic 5 Analyze And Solve Systems Of Linear Equations 43
Answer:

Question 13.
Reason Abstractly A classmate solved the problem using equations with independent variable a and dependent variable b. What do these variables represent in the situation?
Answer:

SEQUEL
Question 14.
Generalize Write an equation or inequality to represent all numbers of flights for which the elevator is faster.
Envision Math Common Core Grade 8 Answers Topic 5 Analyze And Solve Systems Of Linear Equations 44
Answer:

Topic 5 REVIEW

Topic Essential Question
What does it mean to solve a system of linear equations?
Answer:
The solution to a system of linear equations is the point at which the lines representing the linear equations intersect. Two lines in the XY -plane can intersect once, never intersect, or completely overlap.

Vocabulary Review

Complete each definition and then provide an example of each vocabulary word.
Vocabulary
solution of a system of linear equations
system of linear equations
Envision Math Common Core Grade 8 Answers Topic 5 Analyze And Solve Systems Of Linear Equations 45
Answer:

Use Vocabulary in Writing
Describe how you can find the number of solutions of two or more equations by using the slope and the y-intercept. Use vocabulary terms in your description.
Answer:
When slopes and y-intercepts are different, the two lines intersect at one point,
There is only 1 solution.
When slopes are the same, the lines may be either parallel (different y-intercepts)
There are no solutions
If the lines are the same line (Same slopes and same y-intercepts), they intersect at all points,
So, there are infinitely many solutions

Concepts and Skills Review

Lesson 5.1 Estimate Solutions by Inspection

Quick Review
The slopes and y-intercepts of the linear equations in a system determine the relationship between the lines and the number of solutions.
Envision Math Common Core Grade 8 Answers Topic 5 Analyze And Solve Systems Of Linear Equations 46

Example
How many solutions does the system of equations have? Explain.
Answer:
y + 2x = 6
y – 8 = -2x
Write each equation in slope-intercept form.
y = -2x + 6
y = -2x + 8
Identify the slope and y-intercept of each equation.
For the equation, y = -2x + 6, the slope is –2 and the y-intercept is 6.
For the equation, y = -2x + 8, the slope is -2 and the y-intercept is 8.
The equations have the same slope but different y-intercepts, so the system has no solution.

Practice
Determine whether the system of equations has one solution, no solution, or infinitely many solutions.
Question 1.
y – 13 = 5x
y – 5x = 12
Answer:
The given system of equations are:
y – 13 = 5x
y – 5x = 12
So,
The required system of equations are:
y = 5x + 13 —– (1)
y = 5x + 12 —– (2)
Now,
Compare the above equations with
y = mx + b
So,
For the first equation,
m = 5, b = 13
For the second equation,
m = 5, b = 12
We know that,
When slopes are the same, the lines may be either parallel (different y-intercepts)
There are no solutions
Hence, from the above,
We can conclude that there is no solution for the given system of equations

Question 2.
y = 2x + 10
3y – 6x = 30
Answer:
The given system of equations are:
y = 2x + 10 —– (1)
3y – 6x = 30 —– (2)
So,
Divide eq (2) by 3
y – 2x = 10
So,
y = 2x + 10 —– (3)
Now,
Compare the above equations with
y = mx + b
So,
For the first equation,
m = 2, b = 10
For the third equation,
m = 2, b = 10
We know that,
If the lines are the same line (Same slopes and same y-intercepts), they intersect at all points,
So, there are infinitely many solutions
Hence, from the above,
We can conclude that there are infinitely many solutions for the given system of equations

Question 3.
-3x + \(\frac{1}{3}\)y = 12
2y = 18x + 72
Answer:
The given system of equations are:
-3x + \(\frac{1}{3}\)y = 12 —– (1)
2y = 18x + 72 —- (2)
So,
Multiply eq (1) with 3
-9x + y = 36
y = 9x + 36 —– (3)
Now,
Divide eq (2) with 2
So,
y = 9x + 36 —– (4)
Now,
Compare the above equations with
y = mx + b
So,
From the third equation,
m = 9, b = 36
From the fourth equation,
m = 9, b = 36
We know that,
If the lines are the same line (Same slopes and same y-intercepts), they intersect at all points,
So, there are infinitely many solutions
Hence, from the above,
We can conclude that there are infinitely many solutions for the given system of equations

Question 4.
y – \(\frac{1}{4}\)x = -1
y – 2 = 4x
Answer:
The given system of equations are:
y – \(\frac{1}{4}\)x = -1 —- (1)
y – 2 = 4x —— (2)
Now,
y = \(\frac{1}{4}\)x – 1 —- (3)
y = 4x + 2 —- (4)
Compare the above equations with
y = mx + b
So,
From the third equation,
m = \(\frac{1}{4}\), b = -1
From the fourth equation,
m = 4, b = 2
We know that,
When slopes and y-intercepts are different, the two lines intersect at one point,
There is only 1 solution.
Hence, from the above,
We can conclude that there is only 1 solution for the given system of equations

Question 5.
Michael and Ashley each buy x pounds of turkey and y pounds of ham. Turkey costs $3 per pound at Store A and $4.50 per pound at Store B. Ham costs $4 per pound at Store A and $6 per pound at Store B. Michael spends $18 at Store A, and Ashley spends $27 at Store B. Could Michael and Ashley have bought the same amount of turkey and ham? Explain.
Answer:
It is given that
Michael and Ashley each buy x pounds of turkey and y pounds of ham. Turkey costs $3 per pound at Store A and $4.50 per pound at Store B. Ham costs $4 per pound at Store A and $6 per pound at Store B. Michael spends $18 at Store A, and Ashley spends $27 at Store B.
Now,
Take the number of pounds for the turkey to be x and that for the ham to be y
For store A where Michael spent $18,
Turkey cost $3 per pound —- 3x
Ham cost $4 per pound——4y
So,
The equation for cost will be;
3x + 4y = 18
Now,
For store B where Ashley spent $27
Turkey cost $4.5 per pound
Ham cost $6 per pound
So,
The equation for cost is:
4.5x + 6y = 27
So,
The two equations are;
3x + 4y = 18 —— (1)
4.5x + 6y = 27 —– (2)
Now,
Divide eq (2) with 3
So,
1.5x + 2y = 9 —- (3)
Multiply the above equation with 2
So,
3x + 4y = 18 — (4)
Now,
Compare eq (1) and eq (4) with
y = mx + b
So,
From the eq (1),
m = 3, b = 4
From the eq (2),
m = 3, b = 4
From the above,
We can observe that the slopes and the y-intercepts are equal
So,
Both the equations are in the same line
Hence, from the above,
We can conclude that Michael and Ashley bought the same amount of Turkey and Ham

Lesson 5.2 Solve Systems by Graphing

Quick Review
Systems of equations can be solved by looking at their graphs. A system with one solution has one point of intersection. A system with infinitely many solutions has infinite points of intersection. A system with no solution has no points of intersection.

Example
Graph the system and determine its solution.
y = x + 4
y = -2x + 1
Answer:
Graph each equation in the system on the same coordinate plane.
Envision Math Common Core Grade 8 Answers Topic 5 Analyze And Solve Systems Of Linear Equations 47
The point of intersection is (-1, 3). This means the solution to the system is (-1, 3).

Practice
Graph each system and find the solution(s).
Question 1.
y = \(\frac{1}{2}\)x + 1
-2x + 4y = 4
Envision Math Common Core Grade 8 Answers Topic 5 Analyze And Solve Systems Of Linear Equations 48
Answer:
The given system of equations are:
y = \(\frac{1}{2}\)x + 1
-2x + 4y = 4
So,
The representation of the given system of equations in a coordinate plane is:

Hence, from the above,
We can conclude that the given system of equations has infinitely many solutions

Question 2.
y = -x – 3
y + x = 2
Envision Math Common Core Grade 8 Answers Topic 5 Analyze And Solve Systems Of Linear Equations 48
Answer:
The given system of equations are:
y = -x – 3
y + x = 2
So,
The representation of the given system of equations in the coordinate plane is:

Hence, from the above,
We can conclude that there is no solution for the given system of equations

Question 3.
2y = 6x + 4
y = -2x + 2
Envision Math Common Core Grade 8 Answers Topic 5 Analyze And Solve Systems Of Linear Equations 48
Answer:
The given system of equations are:
2y = 6x + 4
y = -2x + 2
So,
The representation of the given system of equations in the coordinate plane is:

Hence, from the above,
We can conclude that the solution for the given system of equations is: (0, 2)

Lesson 5.3 Solve Systems by Substitution

Quick Review
To solve a system by substitution, write one equation for a variable in terms of the other. Substitute the expression into the other equation and solve. If the result is false, the system has no solution. If true, it has infinitely many solutions. If the result is a value, substitute to solve for the other variable.

Example
Use substitution to solve the system.
y = x + 1
y = 5x – 3
Answer:
Substitute x + 1 for y in the second equation.
(x + 1) = 5x – 3
4 = 4x
1 = x
Substitute 1 for x in the first equation.
y = (1) + 1 = 2
The solution is x = 1, y = 2.

Practice
Use substitution to solve each system.
Question 1.
-3y = -2x – 1
y = x – 1
Answer:
The given system of equations are:
-3y = -2x – 1 —– (1)
y = x – 1 —- (2)
Now,
Substitute eq (2) in eq (1)
So,
-3 (x – 1) = -2x – 1
-3 (x) + 3 (1) = -2x – 1
-3x + 3 = -2x – 1
-3x + 2x = -1 – 3
-x = -4
x = 4
So,
y = x – 1
y = 4 – 1
y = 3
Hence, from the above,
We can conclude that the solution for the given system of equations is: (4, 3)

Question 2.
y = 5x + 2
2y – 4 = 10x
Answer:
The given system of equations are:
y = 5x + 2 —- (1)
2y – 4 = 10 —– (2)
Now,
Substitute eq (1) in eq (2)
So,
2 (5x + 2) – 4 = 10
2 (5x) + 2 (2) – 4 = 10
10x = 10
x = 1
So,
y = 5x + 2
y = 5 + 2
y = 7
Hence, from the above,
We can conclude that the solution for the given system of equations is: (1, 7)

Question 3.
2y – 8 = 6x
y = 3x + 2
Answer:
The given system of equations are:
2y – 8 = 6x —- (1)
y = 3x + 2 —– (2)
Now,
Substitute eq (2) in eq (1)
So,
2 (3x + 2) – 8 = 6x
2 (3x) + 2 (2) – 8 = 6x
6x + 4 – 8 = 6x
4 = 8
Hence, from the above,
We can conclude that there is no solution for the given system of equations

Question 4.
2y – 2 = 4x
y = -x + 4
Answer:
The given system of equations are:
2y – 2 = 4x —– (1)
y = -x + 4 —– (2)
Now,
Substitute eq (2) in eq (1)
So,
2 (-x + 4) – 2 = 4x
2 (-x) + 2 (4) – 2 = 4x
-2x + 8 – 2 = 4x
4x + 2x = 6
6x = 6
x = 1
So,
y = -x + 4
y = -1 + 4
y = 3
Hence, from the above,
We can conclude that the solution for the given system of equations is: (1, 3)

Lesson 5.4 Solve Systems by Elimination

Quick Review
To solve a system by elimination, multiply one or both equations to make opposite terms. Add (or subtract) the equations to eliminate one variable. Substitute to solve for the other variable.

Example
Use elimination to solve the system.
2x – 9y = -5
4x – 6y = 2
Multiply the first equation by -2.Then add.
Envision Math Common Core Grade 8 Answers Topic 5 Analyze And Solve Systems Of Linear Equations 49
y = 1
Substitute 1 for y in the first equation.
2x – 9(1) = -5
2x – 9 = -5
2x = 4
x = 2
The solution is x = 2, y = 1.

Practice
Use elimination to solve each system.
Question 1.
-2x + 2y = 2
4x – 4y = 4
Answer:
The given system of equations are:
-2x + 2y = 2 —– (1)
4x – 4y = 4 ——- (2)
So,

Hence, from the above,
We can conclude that the given system of equations has no solution

Question 2.
4x + 6y = 40
-2x + y = 4
Answer:
The given system of equations are:
4x + 6y = 40
-2x + y = 4
So,

Hence, from the above,
We can conclude that the solution for the given system of equations is: (1, 6)

Question 3.
A customer at a concession stand bought 2 boxes of popcorn and 3 drinks for $12. Another customer bought 3 boxes of popcorn and 5 drinks for $19. How much does a box of popcorn cost? How much does a drink cost?
Answer:
It is given that
A customer at a concession stands bought 2 boxes of popcorn and 3 drinks for $12. Another customer bought 3 boxes of popcorn and 5 drinks for $19
Now,
Let each box of popcorn be p
Let each drink be d
So,
For Customer A,
2p + 3d = $12 —– (1)
For Customer B,
3p + 5d = $19 —– (2)
Now,

Hence, from the above,
We can conclude that
The cost of each popcorn box is: $3
The cost of each drink is: $2

Topic 6 Fluency Practice

Pathfinder
Shade a path from START to FINISH. Follow the solutions to the equations from least to greatest. You can only move up, down, right, or left.
I can… solve multistep equations using the Distributive Property.
Envision Math Common Core Grade 8 Answers Topic 5 Analyze And Solve Systems Of Linear Equations 50

enVision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data

Go through the enVision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data and finish your homework or assignments.

enVision Math Common Core 8th Grade Answers Key Topic 4 Investigate Bivariate Data

3-ACT MATH

Reach Out

Reach for the skies! Who in your class can reach the highest? That height depends on how tall each person is and the lengths of their arms.
Now stick your arms out to your sides. Sometimes this horizontal distance is called your wingspan. The wandering albatross can have a wingspan of up to 12 feet. How does your wingspan compare? Think about this during the 3-Act Mathematical Modeling lesson.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 1

enVision STEM Project

Did You Know?
A fishery biologist collects data on fish, such as the size and health of the fish population in a particular body of water.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 2
Largemouth bass and smallmouth bass are the most popular game fish in North America.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 4
Biologists often use tagging studies to estimate fish population, as well as to estimate catch and harvest rates.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 3
The average lifespan of bass is about 16 years, but some have lived more than 20 years.

Research suggests that bass can see red better than any other color on the spectrum.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 5

Your Task: How Many Fish?

Suppose a fishery biologist takes 500 basses from a lake, tags them, and then releases them back into the water. Several days later, the biologist nets a sample of 200 basses, of which 30 are tagged. How many basses are in the lake? You and your classmates will explore how the biologist can use sampling to describe patterns and to make generalizations about the entire population.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 6
Answer:
It is given that
A fishery biologist takes 500 basses from a lake, tags them, and then releases them back into the water. Several days later, the biologist nets a sample of 200 basses, of which 30 are tagged.
So,
The total number of basses = 500 + 200
= 700
The number of basses tagged = 30
So,
After netting, the number of basses = 700 – 30
= 670
Hence, from the above,
We can conclude that after the biologist nets 200 basses,
The total number of basses present are: 670

Topic 4 GET READY!

Review What You Know!

Vocabulary

Choose the best term from the box to complete each definition.

Question 1.
____ is the change in y divided by the change in x.
Answer:
We know that,
“Slope” is the change in y divided by the change in x
Hence, from the above,
We can conclude that the best term to complete the given definition is: Slope

Question 2.
A relationship where for every x units of one quantity there are y units of another quantity is a ____
Answer:
We know that,
A relationship where for every x units of one quantity, there are y units of another quantity is a “Ratio”
Hence, from the above,
We can conclude that the best term to complete the given definition is: Ratio

Question 3.
The ____ is the horizontal line in a coordinate plane.
Answer:
We know that,
The “X-axis” is the horizontal line in a coordinate plane
Hence, from the above,
We can conclude that the best term to complete the given definition is: X-axis

Question 4.
The ___ is the vertical line in a coordinate plane.
Answer:
We know that,
The “Y-axis” is the vertical line in a coordinate plane
Hence, from the above,
We can conclude that the best term to complete the given definition is: Y-axis

Graphing Points
Graph and label each point on the coordinate plane.

Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 7

Question 5.
(-2, 4)
Answer:

Question 6.
(0, 3)
Answer:

Question 7.
(3, -1)
Answer:

Question 8.
(-4, -3)
Answer:

Finding Slope

Find the slope between each pair of points.

Question 9.
(4, 6) and (-2, 8)
Answer:
The given points are: (4, 6), (-2, 8)
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
Slope = y2 – y1 / x2 – x1
So,
Slope = \(\frac{8 – 6}{-2 – 4}\)
= \(\frac{2}{-6}\)
= –\(\frac{1}{3}\)
Hence, from the above,
We can conclude that the slope between the given points is: –\(\frac{1}{3}\)

Question 10.
(-1, 3) and (5,9)
Answer:
The given points are: (-1, 3), (5, 9)
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
Slope = y2 – y1 / x2 – x1
So,
Slope = \(\frac{9 – 3}{5 + 1}\)
= \(\frac{6}{6}\)
= 1
Hence, from the above,
We can conclude that the slope between the given points is: 1

Question 11.
(5, -1) and (-3, -7)
Answer:
The given points are: (5, -1), (-3, -7)
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
Slope = y2 – y1 / x2 – x1
So,
Slope = \(\frac{-7 + 1}{-3 – 5}\)
= \(\frac{-6}{-8}\)
= \(\frac{3}{4}\)
Hence, from the above,
We can conclude that the slope between the given points is: \(\frac{3}{4}\)

Writing Fractions as Percents

Question 12.
Explain how to write \(\frac{36}{60}\) as a percent.
Answer:
The given fraction is: \(\frac{36}{60}\)
We know that,
1 = 100%
So,
\(\frac{36}{60}\)
= \(\frac{36}{60}\) × 100%
= \(\frac{36 × 100%}{60}\)
= 60%
Hence, from the above,
We can conclude that the value of \(\frac{36}{60}\) as a percent is: 60%

Language Development

Complete the graphic organizer. Write the definitions of the terms in your own words. Use words or a sketch to show an example.

Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 9.1
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 9.2
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 9.3
Answer:

Topic 4 PICK A PROJECT

PROJECT 4A

What carnival games do you have a good chance of winning, and why?
PROJECT: BUILD A CARNIVAL GAME
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 9.5

PROJECT 4B
If you had a superpower, what would it be?
PROJECT: SUMMARIZE SUPERHERO DATA
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 9.6

PROJECT 4C
What makes a song’s lyrics catchy?
PROJECT: WRITE A SONG
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 9.7

PROJECT 4D
How does your dream job use math?
PROJECT: RESEARCH A CAREER
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 9.8

Lesson 4.1 Construct and Interpret Scatter Plots

Solve & Discuss It!

Luciana is starting a two-week social media campaign to attract new subscribers to Blaston, a music website for teens. She has the following data from her last campaign to help plan her strategy.

Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 9.9

Look for Relationships
How are the number of media posts and the number of subscribers related?
Answer:
The given data is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 9.9
If we observe the total data,
We can find that there is no particular pattern for the given data
But, if we observe the given data in parts, then
From 1 – 5 posts per day,
Social media posts per day ∝ New subscribers
From 8 – 10 posts per day,
Social media posts per day ∝ \(\frac{1}{New subscribers}\)
From 6 – 7 posts per day,
There is no pattern between the social media posts per day and the number of subscribers

Based on this data, what should be Luciana’s strategy for the new campaign?
Answer:
Based on the pattern of the given data (As mentioned above),
Luciana’s strategy for the new campaign must be:
The social media posts per day and the new subscribers must be in an increasing trend only

Focus on math practices
Use Structure What patterns do you see in the data from Luciana’s last social media campaign?
Answer:
If we observe the total data,
We can find that there is no particular pattern for the given data
But, if we observe the given data in parts, then
From 1 – 5 posts per day,
Social media posts per day ∝ New subscribers
From 8 – 10 posts per day,
Social media posts per day ∝ \(\frac{1}{New subscribers}\)
From 6 – 7 posts per day,
There is no pattern between the social media posts per day and the number of subscribers

Essential Question
How does a scatter plot show the relationship between paired data?
Answer:
The scatter diagram graphs pairs of numerical data, with one variable on each axis, to look for a relationship between them. If the variables are correlated, the points will fall along a line or curve. The better the correlation, the tighter the points will hug the line.

Try It!
Luciana collects data about the number of entries and the ages of the subscribers who enter the concert giveaway.

Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 10.45

The point that represents the data in the fourth column has coordinates Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 10.4
Answer:
The given data is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 10.45
Now,
We know that,
The x-axis always represents the independent variables
The y-axis always represents the dependent variables
So,
From the given data,
The independent variable (x) is: Age
The dependent variable (y) is: Number of entries
We know that,
The ordered pair must be in the form of (x, y)
Hence, from the above,
We can conclude that the point that represents the data in the fourth column has coordinates (13, 9)

Convince Me!
Explain how Luciana would choose scales for the x-axis and y-axis.
Answer:
In a graph,
The scales for the x-axis and the y-axis is nothing but the rate of change between the values of x and y
Ex:
The given data is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 10.45
From the above data,
The scale for the x-axis is:
Rate of change between the values of x = 11 – 10 (or) 12 – 11 and so on
= 1
The scale for the y-axis is:
Rate of change between the values of y = 9 – 8 (or) 10 – 9
= 1
Hence, from the above,
We can conclude that
The scale for the x-axis is:
1 unit = 1 year
The scale for the y-axis is:
1 unit = 1 Entry

Try It!
Avery also tracks the number of minutes a player plays and the number of points the player scored. Describe the association between the two data sets. Tell what the association suggests.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 10.46
Answer:
It is given that
Avery also tracks the number of minutes a player plays and the number of points the player scored.
So,
The given scatter plot is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 10.46
Now,
From the given scatter plot,
We can observe that the overall pattern is in an increasing trend
But,
When we observe the number of points in the perspective of minutes,
The pattern is in clusters
Now,
At 4 minutes,
The number of points scored is: 0
At 6 and 8 minutes,
The number of points scored is: 2
Between 8 and 14 minutes,
The number of points scored is: 4
Between 10 and 16 minutes,
The number of points scored is: 6

KEY CONCEPT

A scatter plot shows the relationship, or association, between two sets of data.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 10.5
The y-values increase as the x-values increase.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 10.6
The y-values decrease as the x-values increase.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 10.7
There is no consistent pattern between the y-values and the x-values.

Do You Understand?

Question 1.
? Essential Question
How does a scatter plot show the relationship between paired data?
Answer:
The scatter diagram graphs pairs of numerical data, with one variable on each axis, to look for a relationship between them. If the variables are correlated, the points will fall along a line or curve. The better the correlation, the tighter the points will hug the line.

Question 2.
Model with Math
Marcy always sleeps fewer than 9 hours each night and has never scored more than 27 points in a basketball game. A scatter plot suggests that the more sleep she gets, the more she scores. What scales for the axes might be best for constructing the scatter plot?
Answer:
It is given that
Marcy always sleeps fewer than 9 hours each night and has never scored more than 27 points in a basketball game. A scatter plot suggests that the more sleep she gets, the more she scores.
So,
The scales for the axes that might be best is:
For the x-axis:
It is given that Macy always sleeps fewer than 9 hours
So,
The scale might be: 1 unit starting from 9 to 24
For the y-axis:
It is given that Macy never scored more than 27 points in a basketball game
So,
The scale might be: 1 unit starting from 27 to the corresponding last value of x
Hence, from the above,
We can conclude that
For the x-axis,
The scale is:
1 unit = 1 hour
For the y-axis,
The scale is:
1 unit = 1 point

Question 3.
Construct Arguments Kyle says that every scatter plot will have a cluster, gap, and outlier. Is he correct? Explain.
Answer:
We know that,
A scatter plot might have a cluster, a gap, and an outlier or the association of any two but not all three are present
Hence, from the above,
We can conclude that Kyle is not correct

Do You Know How?

Question 4.
Phoebe constructs a scatter plot to show the data. What scales could she use for the x- and y-axes?
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 11.1
Answer:
It is given that
Phoebe constructs a scatter plot to show the data.
Note:
The scatter plot is drawn only for the relations that are functions and we know that the rate of change is constant for a function
Now,
The given data is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 11.1
From the given data,
The scale she could use for the x-axis will be 1 unit
The scale she might use for the y-axis will be: 1 unit
Hence, from the above,
We can conclude that
The scale used for the x-axis is:
1 unit = 1 inch (Shoe size)
The scale used for the y-axis is:
1 unit = 1 inch (Height)

Question 5.
Germaine constructs a scatter plot to show how many people visit different theme parks in a month. Why might clusters and outliers be present?
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 11.2
Answer:
It is given that
Germaine constructs a scatter plot to show how many people visit different theme parks in a month
Now,
The given scatter plot is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 11.2
From the given scatter plot,
We can observe that the graph is non-linear
We know that,
A cluster is a group of objects, numbers, data points (information), or even people that are located close together
An outlier is a value in a data set that is very different from the other values. That is, outliers are values unusually far from the middle
So,
From the given scatter plot,
We can observe that there are 2 points that are far from the pattern and those points are called “Outliers”
Since the scatter plot is non-linear, the points will be grouped together and the group of points is called “Clusters”

Practice & Problem Solving

Question 6.
Leveled Practice The table shows the racing times in minutes for the first two laps in a race. Complete the scatter plot.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 11.3
Answer:
It is given that
The table shows the racing times in minutes for the first two laps in a race
Now,
In the graph,
The x-axis represents: The racing times of Lap 1
The y-axis represents: The racing times of Lap 2
Hence,
The completed scatter plot with the x-axis and y-axis is:

Question 7.
The scatter plot represents the prices and number of books sold in a bookstore.
a. Identify the cluster in the scatter plot and explain what it means.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 11.4
Answer:
It is given that
The scatter plot represents the prices and number of books sold in a bookstore.
Now,
The given scatter plot is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 11.4
Now,
We know that,
A cluster is a group of objects, numbers, data points (information), or even people that are located close together
So,
From the above scatter plot,
We can observe that the clusters are present between the intervals of 10 books sold and 20 books sold

b. Generalize How does the scatter plot show the relationship between the data points? Explain.
Answer:
The scatter diagram graphs pairs of numerical data, with one variable on each axis, to look for a relationship between them. If the variables are correlated, the points will fall along a line or curve. The better the correlation, the tighter the points will hug the line.

Question 8.
The table shows the monthly attendance in thousands at museums in one country over a 12-month period.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 12.5
a. Complete the scatter plot to represent the data.
Answer:
It is given that
The table shows the monthly attendance in thousands at museums in one country over a 12-month period.
Now,
The given data is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 12.5
Hence,
The representation of the scatter plot for the given data is:

b. Identify any outliers in the scatter plot.
Answer:
We know that,
A value that “lies outside” (is much smaller or larger than) most of the other values in a set of data is called an “Outlier”
Hence, from the above,
We can conclude that
The outliers in the scatterplot are at (12, 3), (6, 36)

c. What situation might have caused an outlier?
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 12.6
Answer:
From part (b),
The outliers in the scatterplot are at (12, 3), (6, 36)
So,
From the given points,
We can conclude that the number of people is very low at that particular month to cause the situation of outliers

Question 9.
Higher-Order Thinking The table shows the number of painters and sculptors enrolled in seven art schools. Jashar makes an incorrect scatter plot to represent the data.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 12.9
a. What error did Jashar likely make?
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 12.10
Answer:
It is given that
The table shows the number of painters and sculptors enrolled in seven art schools.
Now,
The given data is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 12.9
So,
From the given data,
We can observe that
The variable that will be on the x-axis (Independent variable) is: Number of painters
The variable that will be on the y-axis (Dependent variable) is: Number of sculptors
But,
From the scatter plot drawn by Jashar,
He interchanged the variables of the axes i.e., he took the independent variable at the y-axis and the dependent variable at the x-axis
Hence, from the above,
We can conclude that the error made by Jashar is the interchange of the variables of the axes

b. Explain the relationship between the number of painters and sculptors enrolled in the art schools.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 12.11
Answer:
From the given data,
We can observe that for the increase in painters, the number of sculptors also increases
Hence, from the above,
We can conclude that the relationship between the number of painters and sculptors enrolled in the art schools is:
Number of painters ∝ Number of sculptors

c. Reasoning Jashar’s scatter plot shows two possible outliers. Identify them and explain why they are outliers.
Answer:
We know that,
A value that “lies outside” (is much smaller or larger than) most of the other values in a set of data is called an “Outlier”
Now,
The scatter plot for the given data is:

Hence, from the above,
We can conclude that the two possible outliers identified by Jashar are: (11, 6), and (20, 45)

Assessment Practice

Use the scatter plot to answer 10 and 11.

Question 10.
Ten athletes in the Florida Running Club ran two races of the same length. The scatter plot shows their times. Select all statements that are true.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 12.12
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 12.13 Nine of the times for the first race were at least 16 seconds.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 12.13 Eight of the times for the second race were less than 17 seconds.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 12.13 There were seven athletes who were faster in the second race than in the first.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 12.13 There were three athletes who had the same time in both races.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 12.13 There were three athletes whose times in the two races differed by exactly 1 second.
Answer:
It is given that
Ten athletes in the Florida Running Club ran two races of the same length. The scatter plot shows their times.
Now,
The given scatter plot is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 12.12
Hence,
The correct statements about the given scatter plot is:

Question 11.
What was the greatest difference for a single runner in finishing times in the races?
A. 3 seconds
B. 4 seconds
C. 5 seconds
D. 7 seconds
Answer:
From the given scatter plot,
We can observe that
The lowest time a runner takes for completing a race is approximately 14 seconds
The highest time a runner takes for completing a race is approximately 17 seconds
So,
The greatest difference for a single runner in finishing times in the races is: 3 seconds
Hence, from the above,
We can conclude that option A matches the given situation

Lesson 4.2 Analyze Linear Associations

Solve & Discuss It!

Angus has a big test coming up. Should he stay up and study or go to bed early the night before the test? Defend your recommendation.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 13.1
Answer:
It is given that
Angus has a big test coming up
Now,
The relationship between the sleeping time and the percentage of marks is also given
Now,
From the given data,
We can observe that
If he went to bed early i.e., at 9:00, then he got 93%
If he studied until 11:00, then he got only 92%
Hence, from the above,
We can conclude that Angus has to go to bed early before the big test

Generalize
Can you make a general statement about which option leads to a better result?
Answer:
Generally, going to bed early will lead to better results before a test

Focus on math practices
Construct Arguments What other factors should Angus also take into consideration to make a decision? Defend your response.
Answer:
The other factors that Angus should also take into consideration when making a decision are:
A) Nature of the exam
B) Coverage of the topics for the particular exam
C) Number of revisions

? Essential Question
How can you describe the association of two data sets?
Answer:
Association (or relationship) between two variables will be described as strong, weak, or none; and the direction of the association may be positive, negative, or none

Try It!
Georgia and her classmates also measured their foot length. Use a pencil to find the trend line. Sketch the trend line for the scatter plot.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 13.2
Answer:
It is given that
Georgia and her classmates also measured their foot length
Hence,
The representation of a trend line for the given scatter plot is:

Try It!
For each scatter plot, identify the association between the data. If there is no association, state so.
a.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 13.3

Answer:
The given scatter plot is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 13.3
From the above scatter plot,
We can observe that the points are all scattered
Hence, from the above,
We can conclude that the given scatter plot has a weaker association

b.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 13.4
Answer:
The given scatter plot is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 13.4
From the given scatter plot,
The points are all in a non-linear shape
Hence, from the above,
We can conclude that the given scatter plot has a non-linear association
c.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 13.5
Answer:
The given scatter plot is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 13.5
From the scatter plot,
We can observe that the points are all scattered
Hence, from the above,
We can conclude that the given scatter plot has a weaker association

KEY CONCEPT

Scatter plots can show a linear association, a nonlinear association, or no association. For scatter plots that suggest a linear association, you can draw a trend line to show the association. You can assess the strength of the association by looking at the distances of plotted points from the trend line.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 13.6

Do You Understand?

Question 1.
? Essential Question How can you describe the relationship between the two sets of data?
Answer:
Association (or relationship) between two variables will be described as strong, weak, or none; and the direction of the association may be positive, negative, or none

Question 2.
Look for Relationships How does a trend line describe the strength of the association?
Answer:
The straight line is a trend line, designed to come as close as possible to all the data points. The trend line has a positive slope, which shows a positive relationship between X and Y. The points in the graph are tightly clustered about the trend line due to the strength of the relationship between X and Y.

Question 3.
Construct Arguments How does the scatter plot of a nonlinear association differ from that of a linear association?
Answer:
Scatterplots with a linear pattern have points that seem to generally fall along a line while nonlinear patterns seem to follow along some curve. Whatever the pattern is, we use this to describe the association between the variables.

Do You Know How?

Question 4.
Describe the association between the two sets of data in the scatter plot.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 13.7
Answer:
The given scatter plot is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 13.7
From the given scatter plot,
We can observe that all the points are tightly hugged by a trend line
Hence, from the above,
We can conclude that the given scatter plot has a stronger association

Question 5.
Describe the association between the two sets of data in the scatter plot.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 13.8
Answer:
The given scatter plot is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 13.8
From the given scatter plot,
We can observe that the points are all in a non-linear shape and are closely connected
Hence, from the above,
We can conclude that the given scatter plot has a non-linear association

Practice & Problem Solving

Scan for Multimedia

Question 6.
The scatter plot shows the average heights of children ages 2-12 in a certain country. Which line is the best model of the data?
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 13.9
Answer:
It is given that
The scatter plot shows the average heights of children ages 2-12 in a certain country.
Now,
The best line in the given scatter plot is that line that tightly hugs the maximum points in a scatter plot
Hence, from the above,
We can conclude that line m is the best model of the given data

Question 7.
Does the scatter plot shows a positive, a negative, or no association?
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.1
Answer:
The given scatter plot is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.1
From the given scatter plot,
We can observe that as the value of x increases, the value of y also increases
Hence, from the above,
We can conclude that the given scatter plot has a positive association

Question 8.
Determine whether the scatter plot of the data for the following situation would have a positive or negative linear association.
time working and amount of money earned
Answer:
The given situation is:
Time working and amount of money earned
We know that,
The total amount of work done = Number of days × The amount earned for the work done
Let us suppose the number of days is constant
So,
The total amount of work done ∝ The amount earned for the work done
So,
The more time a person works, the more money that person will earn
Hence, from the above,
We can conclude that the scatter plot of the given data has a positive linear association

Question 9.
Describe the relationship between the data in the scatter plot.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.2
Answer:
The given scatter plot is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.2
From the given scatter plot,
We can observe that the data in the scatter plot has a decreasing trend with the strong association of data with each other
Hence, from the above
We can conclude that the given scatter plot has a negative linear association

Question 10.
Describe the relationship between the data in the scatter plot.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.3
Answer:
The given scatter plot is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.3
From the given scatter plot,
We can observe that all the points are in a cyclic fashion
Hence, from the above,
We can conclude that the given scatter plot has a non-linear association

Question 11.
Higher-Order Thinking Describe a real situation that would fit the relationship described.
a. A strong, positive association
Answer:
The real-life examples for a strong, positive association are:
A) The more time you spend running on a treadmill, the more calories you will burn.
B) Taller people have larger shoe sizes and shorter people have smaller shoe sizes.
C) The longer your hair grows, the more shampoo you will need.
D) The less time I spend marketing my business, the fewer new customers I will have.
E) The more hours you spend in direct sunlight, the more severe your sunburn.

b. A strong, negative association
Answer:
The real-life examples for a strong, negative association are:
A) A student who has many absences has a decrease in grades.
B) As the weather gets colder, air conditioning costs decrease.
C) If a train increases speed, the length of time to get to the final point decreases.
D) If a chicken increases in age, the number of eggs it produces decreases.
E) If the sun shines more, a house with solar panels requires less use of other electricity.

Question 12.
A sociologist is studying how sleep affects the amount of money a person spends. The scatter plot shows the results of the study. What type of association does it show between the amount of sleep and money spent?
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.4
Answer:
It is given that
A sociologist is studying how sleep affects the amount of money a person spends. The scatter plot shows the results of the study
Now,
From the given scatter plot,
We can observe that the data that is related to the amount of sleep and the amount of money spent is in a cyclic fashion
Hence, from the above,
We can conclude that the association does it show between the amount of sleep and money spent is: Non-linear association

Assessment Practice

Question 13.
Which paired data would likely show a positive association? Select all that apply.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.5 Population and the number of schools
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.5 Hair length and shoe size
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.5 Number of people who carpool to work and money spent on gas
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.5 Hours worked and amount of money earned
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.5 Time spent driving and amount of gas in the car
Answer:
We know that,
A positive association is an association that as the value of x increases, the value of y also increases
Hence,
The paired data that would likely show a positive association is

Question 14.
Which paired data would likely show a negative association? Select all that apply.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.5 Population and the number of schools
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.5 Hair length and shoe size
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.5 Number of people who carpool to work and money spent on gas
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.5 Hours worked and amount of money earned
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.5 Time spent driving and amount of gas in the car
Answer:
We know that,
A negative association is an association that as the value of x increases, the value of y also decreases
Hence,
The paired data that would likely show a negative association is:

Lesson 4.3 Use Linear Models to Make Predictions

Solve & Discuss It!

Bao has a new tracking device that he wears when he exercises. It sends data to his computer. How can Bao determine how long he should exercise each day if he wants to burn 5,000 Calories per week?
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 14.6
Answer:
It is given that
Bao has a new tracking device that he wears when he exercises. It sends data to his computer
Now,
It is also given that Bao wants to burn 5,000 calories per week
So,
The number of calories Bao wants to burn per day = \(\frac{5,000}{7}\)
= 714.2 calories
= 714 calories
≅ 720 calories
Now,
From the given scatter plot,
We can observe that
For approximately 720 calories to burn, Bao has to exercise 80 – 90 minutes each day
Hence, from the above,
We can conclude that Bao should exercise 80 – 90 minutes each day if he wants to burn 5,000 Calories per week

Focus on math practices

Reasoning Suppose another set of data were plotted with a trend line passing through (25, 100) and (80, 550). Would this indicate that more or fewer calories were burned per minute? Explain.
Answer:

? Essential Question
How do linear models help you to make a prediction?
Answer:
While linear models do not always accurately represent data, and this occurs when actual data does not clearly show a relationship between its two variables, linear models are helpful in determining the future points of data, the expected points of data, and the highest possible accuracy of data.

Try It!

Assuming the trend shown in the graph continues, use the equation of the trend line to predict average fuel consumption in miles per gallon in 2025.
The equation of the trend line is y = Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 16.1x + Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 16.1. In 2025, the average fuel consumption is predicted to be about mpg.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 16.2
Answer:
The given scatter plot is:
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 16.2
From the scatter plot,
We can observe that
The initial value (y-intercept) is: 15
Now,
We know that,
The equation of the line in the slope-intercept form is:
y = mx + b
Where,
m is the slope
b is the initial value (or) y-intercept
Now,
To find the slope,
The points from the given scatter plot is: (15, 21), (30, 24)
Now,
Compare the given points with (x1, y1), (x2, y2)
We know that,
Slope = y2 – y1 / x2 – x1
So,
Slope = \(\frac{24 – 21}{30 – 15}\)
= \(\frac{1}{5}\)
So,
The equation of the line is:
y = 0.20x + 15
Now,
The average fuel consumption in 2025 is:
y = 0.20 (2025 – 1980) + 15
y = 0.20 (45) + 15
y = 9 + 15
y = 24 mpg
Hence, from the above,
We can conclude that
The equation of the trend line is:
y = 0.20x + 15
In 2025, the average fuel consumption is predicted to be about 24 mpg

Convince Me!
Why can you use a linear model to predict the y-value for a given x-value?
Answer:
We can use the regression line to predict values of Y was given values of X. For any given value of X, we go straight up to the line and then move horizontally to the left to find the value of Y. The predicted value of Y is called the predicted value of Y, and is denoted Y’.

Try It!

A smoothie café has the ingredients needed to make 50,000 smoothies on a day when the high temperature is expected to reach 90°F. Should the café employees expect to have enough ingredients for the day’s smoothie sales? Explain.
Answer:

KEY CONCEPT
Scatter plots can be used to make predictions about current or future trends.
Look for the corresponding y-value for a given x-value.
Envision Math Common Core Grade 8 Answer Key Topic 4 Investigate Bivariate Data 16.3

Find the equation of the trend line and find the y-value of a given x-value.
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 16.4

Do You Understand?

Question 1.
?Essential Question How do linear models help you to make a prediction?
Answer:
While linear models do not always accurately represent data, and this occurs when actual data does not clearly show a relationship between its two variables, linear models are helpful in determining the future points of data, the expected points of data, and the highest possible accuracy of data.

Question 2.
Model with Math
How do you find the equation of a linear model when you are given the graph but not given the equation?
Answer:
To simplify what has already been said, the easiest way to find the equation of a line is to look for the x and y-intercepts.
One point will be (x, 0) and the other will be (0, y), where x and y are numerical values.
The slope is simply
m = \(\frac{y}{x}\).
When you have the y-intercept, (0, y),
you can use the form
y = mx + b to find the equation for the line.
Consequently, with the notation used, you can represent this as
y=\(\frac{y}{x}\)x + b
where b is the value from (0, y)
x is the value from (x, 0)

Question 3.
Reasoning Can the linear model for a set of data that is presented in a scatter plot always be used to make a prediction about any x-value? Explain.
Answer:
Yes, we can use the linear model to predict values of Y was given values of X. For any given value of X, we go straight up to the line and then move horizontally to the left to find the value of Y. The predicted value of Y is called the predicted value of Y, and is denoted Y’.

Do You Know How?

Question 4.
The graph shows a family’s grocery expenses based on the number of children in the family,
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.1
a. Using the slope, predict the difference in the amount spent on groceries between a family with five children and a family with two children.
Answer:
It is given that
The graph shows a family’s grocery expenses based on the number of children in the family,
Now,
The given scatter plot is:
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.1
Now,
From the given scatter plot,
The pair that represents the amount spent on groceries in a family with five children is: (5, 175)
The pair that represents the amount spent on groceries in a family with two children is: (2, 140)
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
Slope = y2 – y1 / x2 – x1
So,
Slope = \(\frac{140 – 175}{2 – 5}\)
Slope = \(\frac{-35}{-3}\)
Slope = \(\frac{35}{3}\)
Hence, from the above,
We can conclude that using the slope, the difference in the amount spent on groceries between a family with five children and a family with two children is: \(\frac{35}{3}\)

b. How many children can you predict a family has if the amount spent on groceries per week is $169.47?
Answer:
From the given scatter plot,
The trend line equation is:
y = 21.08x + 85.15
Now,
It is given that the amount spent on groceries per week is $169.47
So,
169.47 = 21.08x + 85.15
21.08x = 169.47 – 85.15
21.08x = 84.32
x = \(\frac{84.32}{21.08}\)
x = 4
Hence, from the above,
We can predict 4 children in a family if he has the amount spent on groceries per week is $169.47

Practice & Problem Solving

Question 5.
Leveled Practice The scatter plot shows the number of people at a fair based on the outside temperature. How many fewer people would be predicted to be at the fair on a 100°F day than on a 75°F day?
The slope is Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.2
For each degree that the outside temperature increases, the fair attendance decreases by Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.2 thousand people.
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.34
The difference between 75°F and 100°F is Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.2 °F.
-0.16 . Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.2 = Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.2
About Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.2 thousand fewer people are predicted to be at the fair on a 100°F day than on a 75°F day.
Answer:
It is given that
The scatter plot shows the number of people at a fair based on the outside temperature
Now,
The given scatter plot is:
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.34
Now,
We know that,
The equation of the trend line that is passing through two points is:
y = mx + b
Where,
m is the slope
b is the initial value (or) y-intercept
Now,
To find the slope,
The given points are: (75, 10K), (100, 6K)
Where,
K is 1000
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
Slope = y2 – y1 / x2 – x1
So,
Slope = \(\frac{6K – 10K}{100 – 75}\)
= –\(\frac{4,000}{25}\)
= -160
So,
The equation of the trend line is:
y = -160x + b
Substitute (100, 6K) in the above equation
So,
6K = -160 (100) + b
6K + 16K = b
b = 22K
So,
The equation of the trend line is:
y = -160x + 22,000
Now,
At 75° F,
y = -160 (75) + 22,000
y = 10,000
At 100° F,
y = -160 (100) + 22,000
y = 6,000
Hence,
The difference of the people between 75° F and 100° F = 10,000 – 6,000
= 4,000
The difference between 100° F and 75° F = 25° F

Question 6.
Make Sense and Persevere If x represents the number of years since 2000 and y represents the gas price, predict what the difference between the gas prices in 2013 and 2001 is? Round to the nearest hundredth.
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.3
Answer:
It is given that
x represents the number of years since 2000 and y represents the gas price,
Now,
We know that,
The equation of the trend line in the slope-intercept form is:
y = mx + b
Where,
m is the slope
b is the y-intercept
Now,
To find the slope of the trend line,
The given points are: (7, 3), (12, 4)
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
Slope = y2 – y1 / x2 – x1
So,
Slope = \(\frac{4 – 3}{12 – 7}\)
Slope = \(\frac{1}{5}\)
So,
y = \(\frac{1}{5}\)x + b
Now,
Substitute (7, 3) or (12, 4) in the above equation
So,
3 = \(\frac{1}{5}\) (7) + b
\(\frac{8}{5}\) = b
So,
The equation of the trend line is:
5y = x + 8
Now,
The gas prices in 2001 is:
5y = 1 + 8
y = \(\frac{9}{5}\)
y = $1.40
The gas prices in 2013 is:
5y = 13 + 8
y = \(\frac{21}{5}\)
y = $4.20
So,
The difference between the gas prices in 2013 and 2001 = $4.20 – $1.40
= $2.80
Hence, from the above,
We can conclude that the difference between the gas prices in 2013 and 2001 is: $2.80

Question 7.
Make Sense and Persevere If x represents the number of months since the beginning of 2016, and y represents the total precipitation to date, predict the amount of precipitation received between the end of March and the end of June.
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.4
Answer:
It is given that
x represents the number of months since the beginning of 2016, and y represents the total precipitation to date
Now,
The given scatter plot is:
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.4
Now,
From the given scatter plot,
We can observe that the trend line starts from the origin
So,
The equation of the trend line that is passing through the origin is:
y = mx
where,
m is the slope
Now,
To find the slope.
The given points are: (2, 10), (10, 40)
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
Slope = y2 – y1 / x2 – x1
So,
Slope = \(\frac{40 – 10}{10 – 2}\)
= \(\frac{30}{8}\)
= \(\frac{15}{4}\)
So,
The equation of the trend line is:
y = \(\frac{15}{4}\)x
Now,
At the end of the march,
The amount of precipitation is:
y = \(\frac{15}{4}\) (4)
y = 15 in
At the end of June,
The amount of precipitation is:
y = \(\frac{15}{4}\) (6)
y = \(\frac{45}{2}\)
y = 22.5 inches
So,
The amount of precipitation between the end of March and the end of June = 22.5 – 15
= 7.5 in
Hence, from the above,
We can conclude that the amount of precipitation between the end of March and the end of June is: 7.5 in

Question 8.
The scatter plot shows a hiker’s elevation above sea level over time. The equation of the trend line shown is y = 8.77x + 686. To the nearest whole number, predict what the hiker’s elevation will be after 145 minutes.
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.5
Answer:
It is given that
The scatter plot shows a hiker’s elevation above sea level over time.
The equation of the trend line shown is
y = 8.77x + 686.
Where,
8.77 is the slope
686 is the initial value (or) y-intercept
Now,
From the graph,
We can observe that
The x-axis variable – Time
The y-axis variable – Elevation
So,
The hiker’s elevation after 145 minutes is:
y = 8.77 (145) + 686
y = 1,957.65 ft
Hence, from the above,
We can conclude that the hiker’s elevation after 145 minutes will be: 1,957.65 ft

Question 9.
Make Sense and Persevere The graph shows the number of gallons of water in a large tank as it is being filled. Based on the trend line, predict how long it will take to fill the tank with 375 gallons of water.
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.6
Answer:
It is given that
The graph shows the number of gallons of water in a large tank as it is being filled
Now,
The given scatter plot is:
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.6
Now,
From the given scatter plot,
We can observe that
The initial value (or) y-intercept is: 15
Now,
We know that,
The equation of the trend line that has the initial value is:
y = mx + b
Where,
m is the slope
b is the y-intercept (or) initial value
Now,
To find the slope,
The required points are: (1, 30), (0, 15)
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
Slope = y2 – y1 / x2 – x1
So,
Slope = \(\frac{15 – 30}{0 – 1}\)
= \(\frac{-15}{-1}\)
= 15
So,
The equation of the trend line is:
y = 15x + 15
Now,
The time taken to fill 375 gallons of water is:
375 = 15x + 15
15x = 375 – 15
15x = 360
x = \(\frac{360}{15}\)
x = 24 minutes
Hence, from the above,
We can conclude that the time taken to fill 375 gallons of water is: 24 minutes

Question 10.
Higher-Order Thinking The graph shows the temperature, y, in a freezer x minutes after it was turned on. Five minutes after being turned on, the temperature was actually three degrees from what the trend line shows. What values could the actual temperature be after the freezer was on for five minutes?
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.7
Answer:
It is given that
The graph shows the temperature, y, in a freezer x minutes after it was turned on. Five minutes after being turned on, the temperature was actually three degrees from what the trend line shows.
Now,
From the given scatter plot,
We can observe that,
At 5 minutes of time, the freezer temperature is 15°F
So,
At x = 5, y = 15
But,
According to the given information
At x = 5, y = 15 + 3
So,
y = 18°F
Hence, from the above,
We can conclude that the actual temperature after the freezer was on for five minutes is: 18°F

Assessment Practice

Question 11.
The graph shows the altitude above sea level of a weather balloon over time. The trend line passes through the points (0, 453) and (10, 359). Which statements about the graph are true?
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.8 The data show a positive correlation.
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.8 The trend line is -9.4x – 453.
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.8 In general, the balloon is losing altitude.
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.8 The weather balloon started its flight at about 455 feet above sea level.
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.9
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.8 After 4 minutes, the weather balloon had an altitude of about 415 feet above sea level.
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 17.8 After 395 minutes, the weather balloon had an altitude of about 8 feet above sea level.
Answer:
Let the given options be named as A, B, C, D, E and F respectively
It is given that
The graph shows the altitude above sea level of a weather balloon over time.
The trend line passes through the points (0, 453) and (10, 359)
We know that,
The equation of the trend line that is passing through two points is:
y = mx + b
Where,
m is the slope
b is the initial value (or) y-intercept
We know that
The “y-intercept” is the value of y when x= 0
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
Slope = y2 – y1 / x2 – x1
So,
Slope = \(\frac{359 – 453}{10 – 0}\)
= \(\frac{-94}{10}\)
= -9.4
So,
The equation of the trend line is:
y = -9.4x + 453
Hence, from the above,
We can conclude that options C, D, and E matches the given situation

Topic 4 MID-TOPIC CHECKPOINT

Question 1.
Vocabulary How can you use a trend line to determine the type of linear association for a scatter plot? Lesson 4.2
Answer:
The straight line is a trend line, designed to come as close as possible to all the data points. The trend line has a positive slope, which shows a positive relationship between X and Y. The points in the graph are tightly clustered about the trend line due to the strength of the relationship between X and Y.

The scatter plot shows the amount of time Adam spent studying and his test scores. Use the scatter plot for Items 2-4.

Question 2.
What relationship do you see between the amount of time spent studying and the test scores? Is the relationship linear? Lesson 4.1
A. In general, Adam scores higher on a test when he spends more time studying. There is not a linear relationship.
B. In general, Adam scores higher on a test when he spends more time studying. There is a positive linear relationship.
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 20.1
C. In general, Adam scores lower on a test when he spends more time studying. There is a negative linear relationship.
D. In general, Adam scores lower on a test when he spends more time studying. There is no relationship.
Answer:
It is given that
The scatter plot shows the amount of time Adam spent studying and his test scores
Now,
The given scatter plot is:
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 20.1
From the given scatter plot,
We can observe that
The association or correlation is positive and there is a linear relationship
Adam is scoring higher on a test when he is studying for more hours
Hence, from the above,
We can conclude that option B matches the given situation

Question 3.
Use the y-intercept and the point (4,90) from the line on the scatter plot. What is the equation of the linear model? Lesson 4.3
Answer:
The given scatter plot is (From Question 2):
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 20.1
Now,
From the given scatter plot,
We can observe that
The initial value (or) y-intercept is: 60
We know that,
The “y-intercept” is the value of y when x = 0
So,
The points required to find the equation of the scatter plot is: (0, 60), (4, 90)
We know that,
The equation of the trend line that has y-intercept is:
y = mx + b
Where,
m is the slope
b is the initial value (or) y-intercept
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
Slope = y2 – y1 / x2 – x1
So,
Slope = \(\frac{90 – 60}{4 – 0}\)
= \(\frac{30}{4}\)
= \(\frac{15}{2}\)
So,
The equation of the trend line is:
y = \(\frac{15}{2}\)x + 60
Hence, from the above,
We can conclude that the equation of the linear line is:
y = \(\frac{15}{2}\)x + 60

Question 4.
Predict Adam’s test score when he studies for 6 hours. Lesson 4.3
Answer:
We know that,
From the given scatter plot,
The variable on the x-axis is: Time
The variable on the y-axis is: Test scores
Now,
From Problem 3,
The equation of the trend line is:
y = \(\frac{15}{2}\)x + 60
At 6 hours,
y = \(\frac{15}{2}\) (6) + 60
y = 105
Hence, from the above,
We can conclude that Adam’s test score is 105 when he studies for 6 hours

Question 5.
Describe the relationship between the data in the scatter plot. Lesson 4.2
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 20.2
Answer:
The given scatter plot is:
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 20.2
From the above scatter plot,
We can observe that as the value of x increases, the value of y decreases
Hence, from the above,
We can conclude that the given scatter plot has the negative association

Question 6.
The scatter plot shows the mean annual temperature at different elevations. Select all the observations that are true about the scatter plot. Lesson 4.1
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 22.1 The majority of the elevations are in a cluster between 1,250 meters and 2,250 meters.
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 22.1 There is a gap in the data between 500 meters and 1,250 meters.
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 23.1
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 22.1 There is an outlier at about (50, 21).
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 22.1 In general, the mean annual temperature decreases as the elevation increases.
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 22.1 Because there is a gap in the values, there is no association between the temperature and elevation.
Answer:
Let the given options be named as A, B, C, D, and E
It is given that
The scatter plot shows the mean annual temperature at different elevations
Now,
The given scatter plot is:
Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 23.1
From the given scatter plot,
We can observe that
There is a cluster between 1,250 m and 2,250m
There is a gap between 500m and 1,250m
In general, the mean annual temperature decreases as the elevation increases.
Because there is a gap in the values, there is no association between the temperature and elevation.
Hence, from the above,
We can conclude that A, B, D, and E matches the given situation
How well did you do on the mid-topic checkpoint? Fill in the stars. Envision Math Common Core 8th Grade Answers Topic 4 Investigate Bivariate Data 24.1

Topic 4 MID-TOPIC PERFORMANCE TASK

A pitcher’s ERA (earned run average) is the average number of earned runs the pitcher allows every 9 innings pitched. The table shows the ERA and the number of wins for starting pitchers in a baseball league.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 26.1

PART A
Construct a scatter plot of the data in the table.
Answer:
It is given that
A pitcher’s ERA (earned run average) is the average number of earned runs the pitcher allows every 9 innings pitched. The table shows the ERA and the number of wins for starting pitchers in a baseball league.
Now,
The given table is:
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 26.1
Hence,
The representation of the scatter plot for the given data is:

PART B
Identify the association between the data. Explain the relationship between ERA and the number of wins shown in the scatter plot.
Answer:
From the above scatter plot,
We can observe that
As the value of x increases, the value of y decreases
Hence, from the above,
We can conclude that the relationship between ERA and the number of wins as shown in the above scatter plot is a “Negative Correlation”

PART C
Draw a trend line. Write an equation of the linear model. Predict the number of wins of a pitcher with an ERA of 6.
Answer:
We know that,
The equation of the trend line between two points is:
y = mx + b
Where,
m is the slope
b is the initial value (or) y-intercept
Now,
To find the slope,
The points are: (5, 4), (2, 10)
Now,
Compare the given points with (x1, y1), (x2, y2)
Now,
We know that,
Slope = y2 – y1 / x2 – x1
So,
Slope = \(\frac{10 – 4}{2 – 5}\)
= –\(\frac{6}{3}\)
= -2
So,
The equation of the trend line is:
y = -2x + b
Now,
Substitute (5, 4) in the above equation
So,
4 = -2 (5) + b
4 + 10 = b
b = 14
So,
The equation of the trend line is:
y = -2x + 14
Now,
From the given table,
We can observe that
The x-axis variable is: ERA
The y-axis variable is: The number of wins
So,
For x = 6,
y = -2 (6) + 14
y = 14 – 12
y = 2
Hence, from the above,
We can conclude that the number of wins of a pitcher with an ERA of 6 is: 2

Lesson 4.4 Interpret Two-Way Frequency Tables

Explore It!
The owners of a ski resort want to know which is more popular, skiing or snowboarding. The resort conducts a poll, asking visitors their age and which activity they prefer. The results are shown in the table.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 26.2

A. Use the table to describe the visitors polled.
Answer:
It is given that
The owners of a ski resort want to know which is more popular, skiing or snowboarding. The resort conducts a poll, asking visitors their age and which activity they prefer. The results are shown in the table.
Now,
From the given table,
We can observe that the visiters polled are of the age below 35 and above 35
The activities for which the visitors polled are: Skiing, Snowboarding

B. What information can the owners of the resort determine from the data in the table?
Answer:
From the given table,
We can observe that
The number of visitors that had polled for Skiing and snowboarding
Hence, from the above,
We can conclude that the information the owners of the resort determine from the data in the table is the number of visitors that had polled for Skiing and Snowboarding

C. Make a statement that is supported by the data.
Answer:
The statement that is supported by the given data is:
The number of visitors that are over 35 years is the majority who polled for Skiing

Focus on math practices
Model with Math
How else might you display the data to show the relationship between people’s ages and which activity they prefer?
Answer:
The other way to display the data to show the relationship between people’s ages and the activity they prefer is:

Essential Question
How does a two-way frequency table show the relationships between sets of paired data?
Answer:
Two-way frequency tables are a visual representation of the possible relationships between two sets of categorical data. The categories are labeled at the top and the left side of the table, with the frequency (count) information appearing in the four (or more) interior cells of the table.

Try It!
A weatherman asks 75 people from two different cities if they own rain boots. Complete the two-way frequency table to show the results of the survey.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 27.1
Answer:
It is given that
A weatherman asks 75 people from two different cities if they own rain boots.
So,
The total number of people who say whether they own rain boots or not are: 75
So,
(The people who say yes + The people who say no)City A + (The people who say yes + the people who say no)City B = 75
Hence,
The complete two-way frequency table that shows the results of the survey is:

Convince Me!
What pattern do you see in the two-way frequency table?
Answer:
Two-way frequency tables are a visual representation of the possible relationships between two sets of categorical data. The categories are labeled at the top and the left side of the table, with the frequency (count) information appearing in the four (or more) interior cells of the table.

Try It!
One hundred students were asked how they traveled to school. Of the girls, 19 rode in a car, 7 rode the bus, and 27 took the train. Of the boys, 12 took the train, 25 rode in a car, and 10 rode the bus. Construct a two-way frequency table. Then tell which mode of transportation is the most popular. Explain.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 27.2
Answer:
It is given that
One hundred students were asked how they traveled to school. Of the girls, 19 rode in a car, 7 rode the bus, and 27 took the train. Of the boys, 12 took the train, 25 rode in a car, and 10 rode the bus
So,
The complete two-way frequency table for the given situation is:

Now,
From the above, two-way frequency table,
We can observe that more number of people preferred car mode of transportation
Hence, from the above,
We can conclude that the car mode of transportation is the most popular

KEY CONCEPT
A two-way frequency table displays the relationship between paired categorical data. You can interpret the data in the table to draw conclusions.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 27.3

Do You Understand?

Question 1.
?Essential Question How does a two-way frequency table show the relationship between sets of paired categorical data?
Answer:
Two-way frequency tables are a visual representation of the possible relationships between two sets of categorical data. The categories are labeled at the top and the left side of the table, with the frequency (count) information appearing in the four (or more) interior cells of the table.

Question 2.
Model with Math
How do you decide where to start filling in a two-way frequency table when some of the data are already there?
Answer:
In a two-way frequency table, when there is already data present,
You have to start filling in where there is more data in the table so that all the frequencies can be counted easily and filling of the frequency table will also be fast

Question 3.
Use Structure How can you use the structure of a two-way frequency table to complete it?
Answer:
The steps that are used to complete the two-way frequency table is:
Step 1:
Identify the variables. There are two variables of interest here: the commercial viewed and opinion
Step 2:
Determine the possible values of each variable. For the two variables, we can identify the following possible values
Step 3:
Set up the table
Step 4:
Fill in the frequencies

Do You Know How?

Question 4.
A basketball coach closely watches the shots of 60 players during basketball tryouts. Complete the two-way frequency table to show her observations.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 30.1
Answer:
It is given that
A basketball coach closely watches the shots of 60 players during basketball tryouts.
So,
Underclassmen + Upperclassmen = 60
Hence,
The complete two-way frequency table that shows the basketball coach’s observations is:

Question 5.
Do the data in the two-way frequency table support the following statement? Explain.
There are more middle school students who wear glasses than high school students who wear contacts.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 30.2
Answer:
The given statement is:
There are more middle school students who wear glasses than high school students who wear contacts.
Now,
The given two-way frequency table is:
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 30.2
From the given two-way frequency table,
The number of middle school students who wear glasses is: 13
The number of high school students who wear contacts is: 20
So,
The number of middle school students who wear glasses < The number of high school students who wear contacts
Hence, from the above,
We can conclude that the given statement can’t be supported

Practice & Problem Solving

Leveled Practice in 6-8, complete the two-way frequency tables.

Question 6.
You ask 70 of your classmates if they have any siblings. Complete the two-way frequency table to show the results of the survey.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 30.3
Answer:
It is given that
You ask 70 of your classmates if they have any siblings
So,
(The number of boys and girls who have siblings) + (The number of girls who do not have siblings) = 70
Hence,
The complete two-way frequency table that shows the survey results is:

Question 7.
A company surveyed 200 people and asked which car model they preferred. Complete the two-way frequency table to show the results of the survey.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 30.4
Answer:
It is given that
A company surveyed 200 people and asked which car model they preferred
So,
(The number of males and females who preferred 2-door car model) + (The number of males and females who preferred 4-door car model) = 200
Hence,
The complete two-way frequency table that shows the results of the survey is:

Question 8.
Make Sense and Persevere
You ask 203 of your classmates how they feel about the school year being made longer. Complete the two-way frequency table to show the results of the survey.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 30.5
Answer:
It is given that
You ask 203 of your classmates how they feel about the school year being made longer
So,
6th Grade students + 7th Grade students + 8th Grade students = 203
Hence,
The complete two-way frequency table that shows the complete survey results is:

Question 9.
Students at a local school were asked, “About how many hours do you spend on homework each week?” The two-way frequency table shows the results of the survey. Classify the statement below as true or false. Explain.
More students study for 5 to 6 hours than for 1 to 2 hours.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 30.6
Answer:
It is given that
The two-way frequency table shows the results of the survey.
Now,
The given statement is:
More students study for 5 to 6 hours than for 1 to 2 hours.
Now,
The given two-way frequency table is:
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 30.6
From the given two-way frequency table,
We can observe that
The number of students who study for 5 – 6 hours is: 104
The number of students who study for 1 – 2 hours is: 147
So,
The number of students who study for 1 – 2 hours > The number of students who study for 5 – 6 hours
Hence, from the above,
We can conclude that the given statement is false

Question 10.
Higher-Order Thinking Demi and Margaret record the weather in their respective cities on weekend days over the summer. a. Construct a single, two-way frequency table to show the results.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 30.7
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 30.8
Answer:
It is given that
Demi and Margaret record the weather in their respective cities on weekend days over the summer
Now,
The given information regarding the given situation is:
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 30.8
Let the struck lines be the number of times that have no rain
Let the non-struck lines be the number of lines that have rain
Hence,
The complete two-way frequency table that shows the results is:

b. Which day saw the least rain? Explain.
Answer:
The condition for the least rain is: The number of times rain occurs + The number of times that no rain occurs
Hence, from the above,
We can conclude that Saturday saw the least rain

Assessment Practice

Question 11.
At one point last year, the local animal shelter had only cats and dogs. There were 74 animals in all. Of the cats, 25 were male and 14 were female. Of the dogs, 23 were male and 12 were female.
PART A
Construct a two-way frequency table of
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 40.1
Answer:
It is given that
At one point last year, the local animal shelter had only cats and dogs. There were 74 animals in all. Of the cats, 25 were male and 14 were female. Of the dogs, 23 were male and 12 were female.
Hence,
The complete two-way table that shows the survey results is:

PART B
For which gender, male or female, is there the data.
a greater need for pet adoption? Explain.
A. There are almost twice as many female pets, so there is a greater need for people to adopt female dogs and cats.
B. There are almost twice as many male pets, so there is a greater need for people to adopt male dogs and cats.
C. There are almost twice as many female pets, so there is a greater need for people to adopt male dogs and cats.
D. There are almost twice as many male pets, so there is a greater need for people to adopt female dogs and cats.
Answer:
From part (A),
the two-way frequency table that matches the given situation is:

So,
From the above two-way frequency table,
We can observe that
There are almost twice as males as females
Hence, from the above,
We can conclude that option D matches the given situation perfectly

Lesson 4.5 Interpret TwoWay Relative Frequency Tables

Solve & Discuss It!

Mr. Day’s math class asked 200 cell phone owners which size phone they prefer. They presented the results in a two-way frequency table. How can you use the data to compare the percent of students who chose the small screen to the percent of adults who chose the small screen?
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 42.1
Answer:
It is given that
Mr. Day’s math class asked 200 cell phone owners which size phone they prefer. They presented the results in a two-way frequency table
Now,
From the given two-way frequency table,
We can observe that
The number of students who chose the small screen is: 48
The number of adults who chose the small screen is: 18
Now,
The percent of students who chose the small screen = \(\frac{The number of small screens chosen by the students}{The total number of screens}\) × 100
= \(\frac{48}{200}\) × 100
= 24%
The percent of adults who chose the small screen = \(\frac{The number of small screens chosen by the adults}{The total number of screens}\) × 100
= \(\frac{18}{200}\) × 100
= 9%
So,
The percent of students who chose the small screen to the percent of adults who chose the small screen
= \(\frac{9}{24}\) × 100
= \(\frac{9 × 100}{24}\)
= 37.5%
Hence, from the above,
We can conclude that the percent of students who chose the small screen to the percent of adults who chose the small screen is: 37.5%

Make Sense and Persevere
How do two-way frequency tables allow you to interpret relationships between categorical data using rows and columns?
Answer:
Two-way frequency tables are a visual representation of the possible relationships between two sets of categorical data. The categories are labeled at the top and the left side of the table, with the frequency (count) information appearing in the four (or more) interior cells of the table.

Focus on math practices
Make Sense and Persevere How does know a percentage change the way you interpret the results?
Answer:
First: work out the difference (increase) between the two numbers you are comparing. Then: divide the increase by the original number and multiply the answer by 100.
So,
% increase = Increase ÷ Original Number × 100.
If your answer is a negative number, then this is a percentage decrease.

? Essential Question
What is the advantage of a two-way relative frequency table for showing relationships between sets of paired data?
Answer:
Two-way relative frequency tables show us percentages rather than counts. They are good for seeing if there is an association between two variables

Try It!
Asha asked 82 classmates whether they play sports on the weekend. The results are shown in the two-way frequency table below.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 60.1

Convince Me!
How is a two-way relative frequency table different from a two-way frequency table?
Answer:
When a two-way table displays percentages or ratios (called relative frequencies), instead of just frequency counts, the table is referred to as a two-way relative frequency table. These two-way tables can show relative frequencies for the whole table, for rows, or for columns.

Use Asha’s two-way frequency table to complete the two-way relative frequency table.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 60.2
Answer:
The given two-way table is:
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 60.1
Now,
We know that,
The % of boys or girls who say yes = \(\frac{The number of boys or girls who say yes}{The total number of people}\) × 100
The % of boys or girls who say no = \(\frac{The number of boys or girls who say no}{The total number of people}\) × 100
From the given two-way frequency table,
The total number of people is: 82
Hence,
The complete two-way relative frequency table for the given situation is:

Try It!
Use the data in the table below.

a. How does the percent of students who choose e-books compare to the percent of students who choose audiobooks?
Answer:
From the given two-way relative frequency table,
We can observe that
The % of students who choose e-books is: 52%
The % of students who choose Audiobooks is: 48%
So,
The % of students who choose e-books to the % of students who choose audiobooks
= \(\frac{48}{52}\) × 100
= 92.3%
Hence, from the above,
We can conclude that the % of students who choose e-books to the % of students who choose audiobooks is: 92.3%

b. Is there evidence that 7th graders have a greater tendency to choose audiobooks? Explain.
Answer:
From the given two-way relative frequency table,
The % of 7th-grade students who choose audiobooks is: 58.9%
The % of the 6th-grade students who choose audiobooks is: 36.5%
So,
The % of 7th-grade students who choose audiobooks > The % of 6th-grade students who choose audiobooks
Hence, from the above,
We can conclude that there is a piece of evidence that 7th-graders have a greater tendency to choose audiobooks

KEY CONCEPT
Relative frequency is the ratio of a data value to the total of a row, a column, or the entire data set. It is expressed as a percent. A total two-way relative frequency table gives the percent of the population that is in each group.
In a row two-way relative frequency table, the percents in each row add up to 100%.
In a column two-way relative frequency table, the percents in each column add up to 100%.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 60.3

Do You Understand?

Question 1.
? Essential Question
What is the advantage of a two-way relative frequency table for showing relationships between sets of paired data?
Answer:
Two-way relative frequency tables show us percentages rather than counts. They are good for seeing if there is an association between two variables

Question 2.
Reasoning when comparing relative frequency by rows or columns only, why do the percentages not total 100%? Explain.
Answer:
When comparing relative frequency by rows or columns only, the individual percentages will not be 100%
So, their total will also not be equal to 100%

Question 3.
Critique Reasoning
Maryann says that if 100 people are surveyed, the frequency table will provide the same information as a total relative frequency table. Do you agree? Explain why or why not.
Answer:
It is given that
Maryann says that if 100 people are surveyed, the frequency table will provide the same information as a total relative frequency table
We know that,
The “Two-way frequency table” gives us information about the categories in the form of counts and frequencies
The “Two-way relative frequency table” gives us information about the categories in terms of percentages of frequencies
Hence, from the above,
We can agree with Maryann

Do You Know How?

In 4-6, use the table. Round to the nearest percent.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 70.1

Question 4.
What percent of the people surveyed have the artistic ability?
Answer:
From the table,
The number of people who have the artistic ability is: 101
Now,
We know that,
The % of the people surveyed that have the artistic ability = \(\frac{The total number of people who have the artistic ability}{The total number of people}\) × 100
= \(\frac{101}{223}\) × 100
= 45%
Hence, from the above,
We can conclude that 45% of the people surveyed have the artistic ability

Question 5.
What percent of left-handed people surveyed have the artistic ability?
Answer:
From the table,
The number of left-handed people who have artistic ability is: 86
Now,
We know that,
The % of the left-handed people surveyed that have the artistic ability = \(\frac{The total number of left-handed people who have the artistic ability}{The total number of people}\) × 100
= \(\frac{86}{223}\) × 100
= 39%
Hence, from the above,
We can conclude that 39% of the left-handed people surveyed have the artistic ability

Question 6.
What percent of the people who have the artistic ability are left-handed?
Answer:
From the table,
The number of left-handed people who have artistic ability is: 86
Now,
We know that,
The % of the left-handed people surveyed that have the artistic ability = \(\frac{The total number of left-handed people who have the artistic ability}{The total number of people}\) × 100
= \(\frac{86}{223}\) × 100
= 39%
Hence, from the above,
We can conclude that 39% of the left-handed people surveyed have the artistic ability

Practice & Problem Solving

Leveled Practice in 7-8, complete the two-way relative frequency tables.

Question 7.
In a group of 120 people, each person has a dog, a cat, or a bird. The two-way frequency table shows how many people have each kind of pet. Complete the two-way relative frequency table to show the distribution of the data with respect to all 120 people. Round to the nearest tenth of a percent.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 80.1
Answer:
It is given that
In a group of 120 people, each person has a dog, a cat, or a bird. The two-way frequency table shows how many people have each kind of pet
Hence,
The complete two-way relative frequency table for the given situation is:

Question 8.
There are 55 vehicles in a parking lot. The two-way frequency table shows data about the types and colors of the vehicles. Complete the two-way relative frequency table to show the distribution of the data with respect to color. Round to the nearest tenth of a percent.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 80.2
Answer:
It is given that
There are 55 vehicles in a parking lot. The two-way frequency table shows data about the types and colors of the vehicles.
Hence,
The completed two-way relative frequency table that shows the distribution of the data with respect to color is:

Question 9.
Men and women are asked what type of car they own. The table shows the relative frequencies with respect to the total population asked. Which type of car is more popular?
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 80.5
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 80.6
Answer:
It is given that
Men and women are asked what type of car they own. The table shows the relative frequencies with respect to the total population asked.
Now,
The given two-way relative frequency table is:
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 80.6
Now,
From the given table,
We can observe that
Most of the people have shown interest in the 4-door type of car
Hence, from the above,
We can conclude that the 4-door type of car is more popular

Question 10.
Make Sense and Persevere Students were asked if they like raspberries. The two-way relative frequency table shows the relative frequencies with respect to the response.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 80.7
a. What percent of students who do not like raspberries are girls?
Answer:
It is given that
Students were asked if they like raspberries. The two-way relative frequency table shows the relative frequencies with respect to the response.
Now,
From the given two-way frequency table,
We can observe that the % of girls who do not like raspberries are: 48%
Hence, from the above,
We can conclude that the % of students who do not like raspberries are girls is: 48%

b. Is there evidence of an association between the response and the gender? Explain.
Answer:
From the given two-way relative frequency table,
We can observe that
The % of girls who like raspberries is more than the % of boys who like raspberries
The % of girls who do not like raspberries is less than the % of boys who do not like raspberries

Question 11.
Higher-Order Thinking All the workers in a company were asked a survey question. The two-way frequency table shows the responses from the workers in the day shift and night shift.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 80.8
a. Construct a two-way relative frequency table to show the relative frequencies with respect to the shift.
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 80.9
Answer:
It is given that
All the workers in a company were asked a survey question. The two-way frequency table shows the responses from the workers in the day shift and night shift.
Now,
The given two-way frequency table is:
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 80.8
Hence,
The completed two-way relative frequency table for the survey is:

b. Is there evidence of an association between the response and the shift? Explain.
Answer:
From the two-way frequency table that is mentioned in part (a),
We can observe that
The % of people who opted for the day shift are more than the % of people who opted for the night shift

Assessment Practice

Question 12.
Patients in a blind study were given either Medicine A or Medicine B. The table shows the relative frequencies
Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 80.11
Is there evidence that improvement was related to the type of medicine? Explain.
A. The same number of people took each medicine, but the percent of people who reported improvement after taking Medicine B was significantly greater than the percent for Medicine A.
B. The same number of people took each medicine, but the percent of people who reported
improvement after taking Medicine A was significantly greater than the percent for Medicine B.
C. Different numbers of people took each medicine, but the percent of people who reported improvement after taking Medicine B was significantly greater than the percent for Medicine A.
D. Different numbers of people took each medicine, but the percent of people who reported improvement after taking Medicine A was significantly greater than the percent for Medicine B.
Answer:
It is given that
Patients in a blind study were given either Medicine A or Medicine B. The table shows the relative frequencies
We know that,
The number of people will be different
Now,
When we observe the given two-way related frequency table,
The improvement due to Medicine B > The improvement due to Medicine A
Hence, from the above,
We can conclude that option C matches the given situation

3-Act Mathematical Modeling: Reach Out

3-ACT MATH

Envision Math Common Core Grade 8 Answers Topic 4 Investigate Bivariate Data 100

ACT 1

Question 1.
After watching the video, what is the first question that comes to mind?
Answer:

Question 2.
Write the Main Question you will answer.
Answer:

Question 3.
Construct Arguments Predict an answer to this Main Question. Explain your prediction.
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 90.1
Answer:

Question 4.
On the number line below, write a number that is too small to be the answer. Write a number that is too large.
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 90.2
Answer:

Question 5.
Plot your prediction on the same number line.
Answer:

ACT 2

Question 6.
What information in this situation would be helpful to know? How would you use that information?
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 90.3
Answer:

Question 7.
Use Appropriate Tools What tools can you use to solve the problem? Explain how you would use them strategically.
Answer:

Question 8.
Model with Math
Represent the situation using mathematics. Use your representation to answer the Main Question.
Answer:

Question 9.
What is your answer to the Main Question? Is it higher or lower than your initial prediction? Explain why.
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 91.2
Answer:

ACT 3

Question 10.
Write the answer you saw in the video.
Answer:

Question 11.
Reasoning Does your answer match the answer in the video? If not, what are some reasons that would explain the difference?
Answer:

Question 12.
Make Sense and Persevere Would you change your model now that you know the answer? Explain.
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 92.1
Answer:

Reflect

Question 13.
Model with Math
Explain how you used a mathematical model to represent the situation. How did the model help you answer the Main Question?
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 93.1
Answer:

Question 14.
Critique Reasoning Choose a classmate’s model. How would you adjust that model?
Answer:

SEQUEL

Question 15.
Model with Math Measure a classmate’s wingspan. Use your model to predict your classmate’s height. How well did your model predicts your classmate’s actual height?
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 94.1
Answer:

Topic 4 REVIEW

? Topic Essential Question

How can you represent the relationship between paired data and use the representation to make predictions?
Answer:
The scatter diagram graphs pairs of numerical data, with one variable on each axis, to look for a relationship between them. If the variables are correlated, the points will fall along a line or curve. The better the correlation, the tighter the points will hug the line

Vocabulary Review

Match each example on the left with the correct word and then provide another example.

Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 94.5

Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 94.6
Answer:

Use Vocabulary in Writing
Describe the scatter plot at the right. Use vocabulary terms in your description.
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 94.7
Answer:
The given scatter plot is:
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 94.7
Now,
From the given scatter plot,
We can observe that
With the help of measurement data, a trend line is drawn
There is a trend line that is not passing through the origin
There is an outlier present in the given scatter plot

Concepts and Skills Review

LESSON 4.1 Construct and Interpret Scatter Plots

Quick Review
A scatter plot shows the relationship between paired measurement data. Scatter plots can be used to interpret data by looking for clusters, gaps, and outliers.

Practice
The table shows the distance in miles and the price of airfare in dollars.
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 94.8

Question 1.
Construct a scatter plot.
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 95.1
Answer:
It is given that
The table shows the distance in miles and the price of airfare in dollars.
Hence,
The representation of the scatter plot that describes the relationship between the price of airfare and distance is:

Question 2.
Is there a relationship between distance and airfare? Explain.
Answer:
From the above scatter plot,
We can observe that there is no association between distance and airfare
Hence, from the above,
We can conclude that there is no relationship between distance and airfare

LESSON 4.2 Analyze Linear Associations

Quick Review
The association between the data in a scatter plot can be linear or nonlinear. A trend line is a line on a scatter plot, drawn near the points, which approximates the association between paired data. If the data are linear, the association can be positive or negative, and strong or weak.

Practice
Identify the association between the data on each scatter plot.

Question 1.
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 96.1
Answer:
The given scatter plot is:
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 96.1
Now,
From the given scatter plot,
We can observe that as the value of x increases, the value of y decreases
Hence, from the above,
We can conclude that there is a negative association between the data in the scatter plot

Question 2.
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 96.2
Answer:
The given scatter plot is:
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 96.2
From the given scatter plot,
We can observe that the data is in a non-linear trend
Hence, from the above,
We can conclude that there is a non-linear association between the data in the scatter plot

LESSON 4.3 Use Linear Models to Make Predictions

Quick Review
To make predictions, substitute known values into the equation of a linear model to solve for an unknown.

Practice
The scatter plot shows the wages of employees.
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 96.11

Question 1.
If an employee earns $570, what is the expected number of copies sold?
Answer:
It is given that
The scatter plot shows the wages of employees.
Now,
The given scatter plot is:
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 96.11
From the given scatter plot,
We can observe that
The equation of the trend line is:
y = 6x + 120
Where,
y is the wages
x is the number of copies sold
Now,
For y = $570,
570 = 6x + 120
6x = 570 – 120
6x = 450
x = \(\frac{450}{6}\)
x = 75
Hence, from the above,
We can conclude that for an employee wage of $570, the number of copies sold is: 75

Question 2.
If an employee sells 100 copies, what is the expected wage?
Answer:
For x = 100,
y = 6x + 120
y = 6 (100) + 120
y = 600 + 120
y = 720
Hence,f rom the above,
We can conclude that
If an employee sells 100 copies, then the expected wage is: $720

LESSON 4.4 Interpret Two-Way Frequency Tables

Quick Review
A two-way frequency table displays the relationship between paired categorical data.

Practice

Question 1.
The two-way frequency table shows the results of a random survey of movies watched by 100 students. Mrs. Leary said that according to the data, girls are more likely than boys to watch movie A. Is the statement true or false? Explain.
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 97.1
Answer:
It is given that
The two-way frequency table shows the results of a random survey of movies watched by 100 students.
Now,
The given statement is:
Mrs. Leary said that according to the data, girls are more likely than boys to watch movie A.
Now,
The given two-way frequency table is:
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 97.1
Now,
From the given two-way frequency table,
We can observe that
The number of girls who watch movie A > The number of boys who watch movie A
Hence, from the above,
We can conclude that the given statement is true

LESSON 4.5 Interpret Two-Way Relative Frequency Tables

Quick Review
Relative frequency is the ratio of a data value to the total of a row, a column, or the entire data set. It is expressed as a percent.

Practice

The two-way table shows the eye color of 200 cats participating in a cat show.
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 98.1

Question 1.
Make a two-way relative frequency table to show the distribution of the data with respect to gender. Round to the nearest tenth of a percent, as needed.
Answer:
It is given that
The two-way table shows the eye color of 200 cats participating in a cat show.
Now,
The given two-way frequency table is:
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 98.1
Hence,
The representation of the two-way relative frequency table that shows the distribution of the data wrt gender is:

Question 2.
What percent of cats that are female have blue eyes?
Answer:
From the above two-way relative frequency table,
We can observe that there are 30% of cats that are females who have blue eyes
Hence, from the above,
We can conclude that the percent of cats that are females and have blue eyes is: 30%

Topic 4 Fluency Practice

Hidden Clue
For each ordered pair, solve the equation to find the unknown coordinate. Then locate and label the corresponding point on the graph. Draw line segments to connect the points in alphabetical order. Use the completed picture to help you answer the riddle below.

Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 99.1
Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 99.2

A (6, -0.5y + 20 – 0.5y = 13). 6, Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 99.6

B (4 – 3x – 7x = -8, 7) Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 99.6, 7

C (2x + 4 – 6x = 24, 5) Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 99.6, 5

D (5x + 6 – 10x = 31, 1) Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 99.6, 1

E (7x – 3 – 3x = 13, -2) Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 99.6, -2

F (4, -12y + 8y – 21 = -5) 4, Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 99.6

G (44 = 6x – 1 + 9x, –5) 4, Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 99.6, -5

H(-5, 4y + 14 – 2y = 4) -5, Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 99.6

I (-5, 15+ y + 6 + 2y = 0) -5, Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 99.6

J (4, 3y + 32 – y = 18) 4, Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 99.6

K (6, 5y + 20 + 3y = -20) 6, Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 99.6

L (9x – 14 – 8x = -8, -1) Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 99.6, -1

M(-3, -5y + 10 – y = -2) -3, Envision Math Common Core 8th Grade Answer Key Topic 4 Investigate Bivariate Data 99.6

N(-13 + x – 5 – 4x = -9, 4)
Answer:
The solutions of the above equations are:

enVision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships

Go through the enVision Math Common Core Grade 8 Answer Key Topic 3 Use Functions to Model Relationships and finish your homework or assignments.

enVision Math Common Core 8th Grade Answers Key Topic 3 Use Functions To Model Relationships

Topic 3 GET READY!

Review What You Know!

Vocabulary
Choose the best term from the box to complete each definition.

Question 1.
The ____ is the ratio of the vertical change to the horizontal change of a line.
Answer:
We know that,
The “Slope” is the ratio of the vertical change to the horizontal change of a line
Hence, from the above,
We can conclude that the best term from the box to complete the given definition is “Slope”

Question 2.
A relationship that can be modeled by the equation y = mx is a ___
Answer:
We know that,
A relationship that can be modeled by the equation y = mx is a “Proportional relationship”
Hence, from the above,
We can conclude that the best term from the box to complete the given definition is “Proportional relationship”

Question 3.
y-value at which a line of a graph crosses the y-axis is called the ___
Answer:
We know that,
y-value at which a line of a graph crosses the y-axis is called the “y-intercept”
Hence, from the above,
We can conclude that the best term from the box to complete the given definition is “y-intercept”

Question 4.
An equation written in the form y = mx + b is called the ___
Answer:
We know that,
An equation written in the form y = mx + b is called the “Linear equation” or the “Slope-intercept form”
Hence, from the above,
We can conclude that the best term from the box to complete the given definition is “Linear equation”(or) the “Slope-intercept form”

Slope and y-Intercept

Find the slope and y-intercept of a line that passes through these points.

Question 5.
(2, 2) and (3, 0)
Answer:
The given points are:
(2, 2), and (3, 0)
Compare the given points with (x1, y1), (x2,y2)
We know that,
Slope(m) = y2 – y1 / x2 – x1
So,
m = \(\frac{0 – 2}{3 – 2}\)
= \(\frac{-2}{1}\)
= -2
We know that,
The linear equation in the slope-intercept form is:
y = mx + c
Where,
m is the slope
c is the y-intercept
We know that,
We can obtain the y-intercept by putting the value of x equal to 0
So,
y = -2x + c
Substitute (3, 0) or (2, 2) in the above equation
So,
0 = -6 + c
So,
c = 6
Hence, from the above,
We can conclude that
The slope of a line that passes through the given points is: -2
The y-intercept of a line is: 6

Question 6.
(1, 5) and (4, 10)
Answer:
The given points are:
(1, 5), and (4, 10)
Compare the given points with (x1, y1), (x2,y2)
We know that,
Slope(m) = y2 – y1 / x2 – x1
So,
m = \(\frac{10 – 5}{4 – 1}\)
= \(\frac{5}{3}\)
We know that,
The linear equation in the slope-intercept form is:
y = mx + c
Where,
m is the slope
c is the y-intercept
We know that,
We can obtain the y-intercept by putting the value of x equal to 0
So,
y = \(\frac{5}{3}\)x + c
Substitute (4, 10) or (1, 5) in the above equation
So,
5 = \(\frac{5}{3}\) + c
So,
c = \(\frac{10}{3}\)
Hence, from the above,
We can conclude that
The slope of a line that passes through the given points is: \(\frac{5}{3}\)
The y-intercept of a line is: \(\frac{10}{3}\)

Question 7.
(8, 2) and (-8,6)
Answer:
The given points are:
(8, 2), and (-8, 6)
Compare the given points with (x1, y1), (x2,y2)
We know that,
Slope(m) = y2 – y1 / x2 – x1
So,
m = \(\frac{6 – 2}{-8 – 8}\)
= \(\frac{4}{-16}\)
= –\(\frac{1}{4}\)
We know that,
The linear equation in the slope-intercept form is:
y = mx + c
Where,
m is the slope
c is the y-intercept
We know that,
We can obtain the y-intercept by putting the value of x equal to 0
So,
y = –\(\frac{1}{4}\)x + c
Substitute (-8, 6) or (8, 2) in the above equation
So,
2 = –\(\frac{1}{4}\) (8) + c
So,
c = 4
Hence, from the above,
We can conclude that
The slope of a line that passes through the given points is: –\(\frac{1}{4}\)
The y-intercept of a line is: 4

Compare Proportional Relationships

Jenna’s mother is shopping for energy drinks in 12-ounce bottles for Jenna’s soccer team. Store A sells a case of 18 bottles for $10. Store B sells a case of 12 bottles for $6. Which store sells the drinks for less? Use the graph to compare the unit costs of the drinks.

Question 8.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 1
Answer:
Jenna’s mother is shopping for energy drinks in 12-ounce bottles for Jenna’s soccer team. Store A sells a case of 18 bottles for $10. Store B sells a case of 12 bottles for $6
Now,
The unit cost rate of a bottle in store A = \(\frac{The cost of 18 bottles}{18}\)
= \(\frac{$10}{18}\)
= $0.55
The unit cost rate of a bottle in store B = \(\frac{The cost of 12 bottles}{12}\)
= \(\frac{$6}{12}\)
= $0.5
So,
The representation of the unit cost rate of a bottle in both stores is:

So,
From the above graph,
We can observe that
The unit cost rate of a bottle in store B < The unit cost rate of a bottle in store A
Hence, from the above,
We can conclude that store B sells the drinks for less cost

Linear Equations

Question 9.
Write the equation for the graph of the line shown.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 3.2
Answer:
The given graph is:
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 3.2
We know that,
The y-intercept is the value of the point that passes through the y-axis
So,
From the graph,
The point that passes through the y-axis is: (0, -6)
So,
The y-intercept is: -6
Now,
To find the slope,
The points are: (2, 2), and (0, -6)
Now,
Compare the given points with (x1, y1), (x2,y2)
We know that,
Slope(m) = y2 – y1 / x2 – x1
So,
m = \(\frac{-6 – 2}{0 – 2}\)
= \(\frac{-8}{-2}\)
= 4
We know that,
The linear equation in the slope-intercept form is:
y = mx + c
So,
y = 4x – 6
Hence, from the above,
We can conclude that the equation of the line for the given graph is:
y = 4x – 6

Language Development

Write key words or phrases associated with each representation. Then write function or not a function on the given lines.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 3.3
Answer:

Topic 3 PICK A PROJECT

PROJECT 3A
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 3.10
What machine could be invented to make your life better?
PROJECT: BUILD A RUBE GOLDBERG MACHINE

PROJECT 3B
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 3.11
What games can you play indoors?
PROJECT: MAKE A MATH
CARD GAME

PROJECT 3C
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 101
What are the steps for fixing a leaky pipe?
PROJECT: PLAN A MAINTENANCE ROUTE

PROJECT 3D
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 102
If you were to make a video game, what kind of game would it be?
PROJECT: DESIGN A VIDEO GAME ELEMENT

Lesson 3.1 Understand Relations and Functions

Solve & Discuss It!

The 10 members of Photography Club want to raise $500, so they will hold a raffle with donated prizes. Jesse proposes that to reach their goal, each member should sell 50 raffle tickets. Alexis proposes that each member should raise $50.
Whose plan would you recommend? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 3.15
RAFFLE TICKETS
$1 1 ticket
$5 6 tickets
$20 25 tickets
Answer:
It is given that
The 10 members of the Photography Club want to raise $500, so they will hold a raffle with donated prizes. Jesse proposes that to reach their goal, each member should sell 50 raffle tickets. Alexis proposes that each member should raise $50.
It is also given that
$1              –       1 ticket
$5              –        6 tickets
$20            –        25 tickets
Now,
According to Jesse’s goal,
Each member should sell 50 raffle tickets to make the total amount of $500
The possible combinations may be:
50 $1 tickets will be sold by each member
Any other combination is not possible
According to Alexis’s plan,
Each member should raise $50 to make the total amount of $500
It is possible and very easy because $50 by each member can be raised in many ways
Hence, from the above,
We can conclude that Alexis’s plan would be recommended

Focus on math practices
Reasoning How are the two plans different? How are they similar?
Answer:
According to Jesse’s goal,
Each member should sell 50 raffle tickets to make the total amount of $500
The possible combinations may be:
50 $1 tickets will be sold by each member
Any other combination is not possible
Now,
According to Alexis’s plan,
Each member should raise $50 to make the total amount of $500
It is possible and very easy because $50 by each member can be raised in many ways

? Essential Question
when is a relation a function?
Answer:
A “Relation” from a set X to a set Y is called a “Function” if and only if each element of X is related to exactly one element in Y.

Try It!
Joe needs to advertise his company. He considers several different brochures of different side lengths and areas. He presents the data as ordered pairs (side length, area).
(4, 24), (5, 35), (8, 24), (2, 20), (9, 27)
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 4.1
Complete the arrow diagram. Is the area of a brochure a function of the side length? Explain.
Answer:
Joe needs to advertise his company. He considers several different brochures of different side lengths and areas. He presents the data as ordered pairs (side length, area).
(4, 24), (5, 35), (8, 24), (2, 20), (9, 27)
We know that,
The ordered pairs can be represented in the form of (x, y)
Where,
x is the input
y is the output
Now,
From the given ordered pairs,
We can observe that for different values of the input, there are different values of output
Note:
If there are the same outputs for the different inputs, then also a relationship is considered a function
So,
The complete arrow diagram for the given ordered pairs are:

Hence, from the above,
We can conclude that the area of the brochure is a function of the side length

Convince Me!
There are two outputs of 24. Does this help you determine whether the relation is a function? Explain.
Answer:
We know that,
If there are the same outputs for the different inputs, then also a relationship is considered a function
Hence, from the above
We can conclude that even for the two outputs of 24, the given relationship is considered a function

Try It!

Frank reverses the ordered pairs to show the heights and ages of the same six students. Is age a function of height? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 4.2
Answer:
It is given that
Frank reverses the ordered pairs to show the heights and ages of the same six students.
Now,
The given table is:
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 4.2
Now,
From the given table,
We can observe that
For different values of age, there are different values of height
Where,
Age —-> Input
Height —> Output
Hence, from the above,
We can conclude that age is a function of height

Try It!
Heather claims that she can tell exactly how long a family was at the museum by how much the family pays for parking. Is Heather correct? Explain.
Answer:
It is given that
Heather claims that she can tell exactly how long a family was at the museum by how much the family pays for parking.
Now,
The table for the given situation is: (Example 3)

Now,
From the table,
We can observe that
There are different costs for the different times in hours
So,
We can say that cost is a function of time
Hence, from the above,
We can conclude that Heather’s claim is correct

KEY CONCEPT
A relation is a function if each input corresponds to exactly one output. You can use an arrow diagram or a table to determine whether a relation is a function.
This relation is a function.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 4.3
This relation is not a function.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 4.4

Do You Understand?

Question 1.
? Essential Question
when is a relation a function?
Answer:
A relation from a set X to a set Y is called a function if and only if each element of X is related to exactly one element in Y

Question 2.
Model with Math
How can you use different representations of a relation to determine whether the relation is a function?
Answer:
Relations can be displayed as a table, a mapping, or a graph. In a table, the x-values and y-values are listed in separate columns. Each row represents an ordered pair: Displaying a relation as a table

Question 3.
Generalize
Is a relation always a function? Is a function always a relation? Explain.
Answer:
All functions are relations, but not all relations are functions. A function is a relation that for each input, there is only one output. Here are mappings of functions. The domain is the input or the x-value, and the range is the output or the y-value.

Question 4.
Is the relation shown below a function? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 4.5
Answer:
The given relation is:
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 4.5
From the given relation,
We can observe that there is the same input for the different outputs,
We know that,
A relation can be considered as a function when the different inputs have different outputs
Hence, from the above,
We can conclude that the given relation is not a function

Question 5.
Is the relation shown below a function? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 4.6
Answer:
The given relation is:
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 4.6
From the given relation,
We can observe that there are different outputs for different inputs
We know that,
A relation can be considered as a function when the different inputs have different outputs
Hence, from the above,
We can conclude that the given relation is a function

Question 6.
Is the relation shown below a function? Explain.
(4,16), (5, 25), (3,9), (6, 36), (2, 4), (1, 1)
Answer:
The given relation is:
(4,16), (5, 25), (3,9), (6, 36), (2, 4), (1, 1)
From the given relation,
We can observe that there are different outputs for different inputs
We know that,
A relation can be considered as a function when the different inputs have different outputs
Hence, from the above,
We can conclude that the given relation is a function

Practice & Problem Solving

Question 7.
The set of ordered pairs (1, 19), (2, 23), (3, 23), (4, 29), (5, 31) represents the number of tickets sold for a fundraiser. The input values represent the day and the output values represent the number of tickets sold on that day.
a. Make an arrow diagram that represents
Answer:
The arrow diagram for the given relation is:

b. is the relation a function? Explain.
Answer:
It is given that
The set of ordered pairs (1, 19), (2, 23), (3, 23), (4, 29), (5, 31) represents the number of tickets sold for a fundraiser. The input values represent the day and the output values represent the number of tickets sold on that day.
Now,
The given relation is:
(1, 19), (2, 23), (3, 23), (4, 29), (5, 31)
From the given relation,
We can observe that there are different outputs for different inputs
We know that,
A relation can be considered as a function when the different inputs have different outputs
Hence, from the above,
We can conclude that the given relation is a function

Question 8.
Does the relation shown below represent a function? Explain.
(-2, 2), (-7, 1), (-3, 9), (3, 4), (-9,5), (-6, 8)
Answer:
The given relation is:
(-2, 2), (-7, 1), (-3, 9), (3, 4), (-9,5), (-6, 8)
From the given relation,
We can observe that there are different outputs for different inputs
We know that,
A relation can be considered as a function when the different inputs have different outputs
Hence, from the above,
We can conclude that the given relation is a function

Question 9.
Is the relation shown in the table a function? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 4.10
Answer:
The given relation is:
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 4.10

From the given relation,
We can observe that there are different outputs for the same inputs
We know that,
A relation can be considered as a function when the different inputs have different outputs
Hence, from the above,
We can conclude that the given relation is not a function

Question 10.
Construct Arguments
During a chemistry experiment, Sam records how the temperature changes over time using ordered pairs (time in minutes, temperature in °C).
(0, 15), (5, 20), (10,50) (15, 80). (20, 100), (25, 100) Is the relation a function? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.1
Answer:
It is given that
During a chemistry experiment, Sam records how the temperature changes over time using ordered pairs (time in minutes, temperature in °C).
(0, 15), (5, 20), (10,50) (15, 80). (20, 100), (25, 100)
We know that,
An ordered pair can be represented as (x, y)
Where,
x is the time
y is the temperature in °C
Now,
The given relation is:
(0, 15), (5, 20), (10,50) (15, 80). (20, 100), (25, 100)
From the given relation,
We can observe that there are different outputs for the different inputs
We know that,
A relation can be considered as a function when the different inputs have different outputs
Hence, from the above,
We can conclude that the given relation is a function

Question 11.
Reasoning
Taylor has tracked the number of students in his grade since third grade. He records his data in the table below. Is the relation a function? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.12
Answer:
It is given that
Taylor has tracked the number of students in his grade since third grade. He records his data in the table
Now,
The given table is:
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.12
From the given table,
We can observe that there are different outputs (People) for the different inputs (Grade)
We know that,
A relation can be considered as a function when the different inputs have different outputs
Hence, from the above,
We can conclude that the given table is a function

Question 12.
James raises chickens. He tracks the number of eggs his chickens lay at the end of each week. Is this relation a function? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.3
Answer:
It is given that
James raises chickens. He tracks the number of eggs his chickens lay at the end of each week
Now,
The given relation is:
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.3
From the given relation,
We can observe that there are different outputs (Eggs) for the different inputs (Weeks)
We know that,
A relation can be considered as a function when the different inputs have different outputs
Hence, from the above,
We can conclude that the given relation is a function

Question 13.
Relations P and Q are shown below.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.4
a. Make an arrow diagram to represent Relation P.
Answer:
The given relation is:
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.4
Hence,
The arrow diagram to represent the relation P is:

Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.5
b. Make an arrow diagram to represent Relation Q.
Answer:
The given relation is:
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.5
Hence,
The arrow diagram to represent the relation Q is:

c. Which relation is a function? Explain.
Answer:
From relation P,
We can observe that there are different outputs for the different inputs
From relation Q,
We can observe that there are different outputs for the same inputs
Hence, from the above,
We can conclude that relation P is a function

Question 14.
Higher-Order Thinking
On a recent test, students had to determine whether the relation represented by the ordered pairs (1, 2), (6, 12), (12, 24), (18, 36) is a function. Bobby drew the arrow diagram on the right and said the relationship was not a function. What error did Bobby most likely make?
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.6
Answer:
It is given that
On a recent test, students had to determine whether the relation represented by the ordered pairs (1, 2), (6, 12), (12, 24), (18, 36) is a function. Bobby drew the arrow diagram on the right and said the relationship was not a function.
Now,
From the given arrow diagram and ordered pairs,
We can observe that
In the arrow diagram, inputs and outputs are reversely represented
Hence, from the above,
We can conclude that the error Bobby most likely made is the reversal of inputs and outputs

Assessment Practice

Question 15.
Write the set of ordered pairs that is represented by the arrow diagram at the right. Is the relation a function? Explain.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.7
Answer:
The given arrow diagram is:
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.7
In the arrow diagram,
The left side represented the inputs and the right side represented the outputs
So,
The representation of the arrow diagram in the form of the ordered pairs (Input, Output) are:
(49, 13), (61, 36), (10, 27), (76, 52), (23, 52)
From the above relation,
We can observe that there are different outputs for the different inputs
We know that,
A relation can be considered as a function when the different inputs have different outputs
Hence, from the above,
We can conclude that the given relation is a function

Question 16.
Which of these relations are functions? Select all that apply.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.8
Answer:
We know that,
A relation can be considered as a function when the different inputs have different outputs
So,
From the given relations,
Relation 2, Relation 3 are the functions
Hence, from the above,
We can conclude that Relation 2 and Relation 3 are the functions

Lesson 3.2 Connect Representations of Functions

Solve & Discuss It!

Eliza volunteers at a nearby aquarium, where she tracks the migratory patterns of humpback whales from their feeding grounds to their breeding grounds. She recorded the distance, in miles, traveled by the whales each day for the first 7-day period of their migration. Based on Eliza’s data, how long will it take the humpback whales to travel the 3,100 miles to their breeding grounds?
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.9

Focus on math practices
Construct Arguments How does finding an average distance the whales travel in miles help with finding a solution to this problem?

? Essential Question
What are different representations of a function?
Answer:
Relationships and functions can be represented as graphs, tables, equations, or verbal descriptions. Each representation gives us certain information. A table of values, mapping diagram, or set of ordered pairs gives us a list of input values and their corresponding output values.

Try It!
As the pump is pumping water, the amount of water in the pool decreases at a constant rate. Complete the statements below. Then graph the function.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.10
The amount of water remaining in the pool is Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.11 gallons.
The amount of water pumped each hour is Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.11 gallons.
The equation is Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.11
Answer:
It is given that
As the pump is pumping water, the amount of water in the pool decreases at a constant rate
Now,
Let the initial amount of water present in the pool is: 9,000 gallons
So,
The rate of the amount of water that pumped each hour = \(\frac{The initial amount of water present in the pool}{The time that is present where the initial amount of water present}\)
= \(\frac{9,000}{12}\)
= 750 gallons per hour
So,
The amount of water remaining in the pool = The initial amount of water present in the pool – The amount of water that pumped each hour
= 9,000 – 1,500
= 7,500 gallons
Let the number of hours be x
We know that,
The linear equation is in the form of
y = mx + c
So,
The total amount of water present in the pool = The rate at which the water pumps out + The amount of water that pumped each hour
9,000 = 750x + 7,500
Hence, from the above,
We can conclude that
The amount of water remaining in the pool is 7,500 gallons.
The amount of water pumped each hour is 1,500 gallons.
The equation is:
9,000 = 750x + 7,500

Convince Me!
How is the rate of change of this function different from that in Example 1? Explain.
Answer:
The rate of change of the function present in Example 1 is increasing at a constant rate whereas the rate of change of the function in this situation is decreasing at a constant rate

Try It!
Draw a graph that represents a linear function?
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.111
Answer:
We know that,
The representation of the linear equation is:
y = mx —–> Slope form
y = mx + c —-> Slope-intercept form
Now,
Let the linear equation in the slope-intercept form be:
y = x + 3
Hence,
The graph of the above linear equation in the coordinate plane is:

KEY CONCEPT

You can represent a function in different ways: in a table, in a graph, or as an equation.
A day at the amusement park costs $10 for an entrance fee and $2.50 for each ride ticket.
Envision Math Common Core Grade 8 Answer Key Topic 3 Use Functions To Model Relationships 5.122

Do You Understand?

Question 1.
?Essential Question What are different representations of a function?
Answer:
Relationships and functions can be represented as graphs, tables, equations, or verbal descriptions. Each representation gives us certain information. A table of values, mapping diagram, or set of ordered pai