1. Insert Lesson Title Here
Course 2
Circumference
Insert Lesson Title Here
Vocabulary
The distance around a circle is called
circumference.

2. CIRCUMFERENCE OF A CIRCLE
Course 2
Circumference
CIRCUMFERENCE OF A CIRCLE
The circumference C of a circle is  times the diameter d, or 2 times the radius r.
Formula
Radius
C = d, or C = 2r
Diameter
Circumference

3. Circumference C = d C  3.14 · 12 C  37.68 Example 1
Course 2
Circumference
Example 1
Find the circumference of the circle to the nearest tenth. Use 3.14 for .
C = d
You know the diameter.
12 in.
C  3.14 · 12
Substitute for  and d.
C  37.68
Multiply.
The circumference of the circle is about 37.7 in.

4. Circumference Example 2
Course 2
Circumference
Example 2
Find the circumference of the circle to the nearest tenth. Use 3.14 for .
C = 2r
You know the radius.
18 cm
C  2 · 3.14 · 18
Substitute for  and r.
C 
Multiply.
The circumference of the circle is about cm.

5. Circumference C = d C  3.14 · 7 C  21.98 Example 3
Course 2
Circumference
Example 3
Find the circumference of the circle to the nearest tenth. Use 3.14 for .
C = d
You know the diameter.
7 in.
C  3.14 · 7
Substitute for  and d.
C  21.98
Multiply.
The circumference of the circle is about 22.0 in.

6. Circumference Example 4
Course 2
Circumference
Example 4
Find the circumference of the circle to the nearest tenth. Use 3.14 for .
C = 2r
You know the radius.
11 cm
C  2 · 3.14 · 11
Substitute for  and r.
C  69.08
Multiply.
The circumference of the circle is about 69.1 cm.

7. Circumference Helpful Hint If the diameter or radius of a circle is a
Course 2
Circumference
If the diameter or radius of a circle is a
multiple of 7, use for p.
Helpful Hint
22 7

8. Circumference for . Example 5: Application
Course 2
Circumference
Example 5: Application
The diameter of a circular pond is 42 m. What is its circumference? Use
for . 22 7
C = d
You know the diameter. 22 7 22 7
C 
· 42
Substitute
for  and 42 for d. 22 7 42 1
C 
Write 42 as a fraction. 6 22 7 42 1
C 
Simplify. 1
C  132
Multiply.
The circumference of the pond is about 132 m.

9. Circumference for . Example 6
Course 2
Circumference
Example 6
The diameter of a circular spa is 14 m. What is its circumference? Use 22 7
for .
C = d
You know the diameter. 22 7 22 7
C 
· 14
Substitute
for  and 14 for d. 22 7 14 1
C 
Write 14 as a fraction. 2 22 7 14 1
C 
Simplify. 1
C  44
Multiply.
The circumference of the spa is about 44 m.

10. Insert Lesson Title Here
Course 2
Circumference
Insert Lesson Title Here
1. If a guardrail is to be placed around the edge
of a circular swimming pool with a diameter of
14 ft, how many feet of railing will be needed?
Use for . 22 7
44 ft

11. Insert Lesson Title Here
Course 2
Circumference
Insert Lesson Title Here
1/20/17
A Ferris wheel has a circumference of 440 feet. What
is the approximate diameter of the Ferris wheel?
140 ft