Name ________________________________________ Date __________________ Class __________________
LESSON
Circumference
9-1
Reteach
The distance around a circle is called the circumference. To find
the circumference of a circle, you need to know the diameter or the
radius of the circle.
The ratio of the circumference of any circle to its diameter ⎛⎜ ⎞⎟
C
⎝d⎠
is always the same. This ratio is known as π (pi) and has a value
of approximately 3.14.
To find the circumference C of a circle if you know the diameter
d, multiply π times the diameter. C = π • d, or C ≈ 3.14 • d.
C=π •d
C ≈ 3.14 • d
C ≈ 3.14 • 6
C ≈ 18.84
The circumference is about 18.8 in.
to the nearest tenth.
The diameter of a circle is twice as long as the radius r, or d = 2r.
To find the circumference if you know the radius, replace d with 2r in
the formula. C = π • d = π • 2r
Find the circumference given the Find the circumference given the radius.
diameter. 2. r = 13 in.
1. d = 9 cm C = π • 2r
C=π •d C ≈ 3.14 • (2 • ________)
C ≈ 3.14 • ________
C ≈ 3.14 • ________
C ≈ ___________
The circumference is ________ cm to C ≈ ___________
the nearest tenth of a centimeter. The circumference is ________ in. to
the nearest tenth of an inch.
Find the circumference of each circle to the nearest tenth.
Use 3.14 for π .
3. 4. 5.
________________________ _______________________ ________________________
Original content Copyright © by Houghton Mifflin Harcourt. Additions and changes to the original content are the responsibility of the instructor.
192
MODULE 9 Circumference, 6. 12.6 yd
Area, and Volume 7. 110 yd
8. 28.3 in.
LESSON 9-1
9. 125.7 cm
Practice and Problem Solving: A/B
Reteach
1. 18.84 in.
1. 9; 28.26; 28.3
2. 56.52 cm
2. 13; 26; 81.64; 81.6
3. 4.71 ft
3. 40.8 cm
4. 25.12 m
4. 31.4 ft
5. 37.68 ft
5. 9.4 in.
6. 12.56 yd
7. 43.96 in. Reading Strategies
8. 26.26 cm 1. C = 2π r
9. 7.85 m 2. C = π d
10. 66 ft 3. It is twice as long.
11. 132 mm 22
4. Sample answer: 3.14 or
12. 88 cm 7
Practice and Problem Solving: C 5. The circumference of a circle is the
distance around a circle. It is given in
1. 3.93 in. units. The perimeter of a polygon is the
2. 11.30 yd distance around a polygon. It is given in
3. 13.19 mm units.
4. 2.36 cm Success for English Learners
5. 4.19 ft 1. the length of the diameter.
6. 3.14 in. 2. 18 cm
7. 3.5 in. 3. Take half of the diameter, 17 ft, and
8. 18 yd substitute that value into the formula for r.
9. 9.55 in. 4. d = 10 so r = 5
10. 16 C = 2π r C = πd
= 2 • 3.14 • 5 = 3.14 • 10
Practice and Problem Solving: D
1. 50.2 m = 31.4 = 31.4
2. 62.8 in.
3. 9.4 ft
4. 22.0 mm
5. 18.8 cm
Original content Copyright © by Houghton Mifflin Harcourt. Additions and changes to the original content are the responsibility of the instructor.
346
