Name ——————————————————————————
LESSON
20.3
G OAL
Date ——————————————
CA Standards
MG 1.1
MG 1.2
Reteach
For use with pages 545–550
Find the circumferences of circles.
VOCABULARY
A circle is the set of all points in a plane that are the same
distance from a fixed point called the center.
The distance from the center to any point on a circle is
the radius.
The distance across a circle through the center is the diameter.
The circumference of a circle is the distance around the circle.
Circumference of a Circle
Words
EX AM PLE
diameter d
8 Lesson 20.3
Algebra
The circumference C of a circle
is the product of and the
diameter, or twice the product
of and the radius.
C d C 2r
radius r
1 Finding the Circumference of a Circle
Find the circumference of the wheel. Use 3.14 for .
Copyright © Houghton Mifflin Company.
C d
3.14(30)
30 in.
Write formula for circumference.
Substitute 3.14 for and 30
for d.
94.2
Multiply.
Answer: The circumference of the wheel is about
94.2 inches.
EX AM PLE
2 Finding the Circumference of a Circle
Find the circumference of the circle. Use 272 for .
Round to the nearest whole number.
C 2r
Write formula for circumference.
22
22 for and 28 for r.
__
Substitute __
2 7 (28)
7
176
Multiply.
Answer: The circumference of the circle is about 176 meters.
28 m
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Name ———————————————————————
LESSON
Reteach
20.3
Date ——————————
continued
For use with pages 545–550
Exercises
for Examples 1 and 2
...................................................................................................
22
Find the circumference of the circle. Use ___
or 3.14 for .
7
1.
2.
3.
22 mm
18 yd
8 in.
4.
5.
6.
120 cm
56 m
Lesson 20.3
91 ft
E X A M P LE
3 Multiple Choice Practice
Solution
C d
Write formula for circumference.
Substitute 49 for d
(49)
Answer: The equation C (49), or C 49 , can be used to find the
C
circumference. The correct answer is C. A
B
D
Exercise
for Example 3
...................................................................................................
7. The radius of a circle is about 56 centimeters. Find the
circumference of the circle in terms of .
Copyright © Houghton Mifflin Company.
The Qutab Minar is a five-story tower in Delhi, India. The base
of the tower is circular with a diameter of about 49 feet. Which
equation can be used to find its circumference?
2
A. C 49 B. C 2 49 C. C 49 D. C 24.5 Reteach
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