1. Circumference of a Circle

2. C = 2r C  Circumference - The distance around a circle
For every circle, the ratio of circumference C to diameter d is the same. This ratio, , is the Greek letter , called pi. C d
Radius 22 7
Pi is approximately equal to 3.14 or .
To find Circumference knowing diameter
Diameter
C = d
To find Circumference knowing radius
C = 2r
Circumference
C 
To find Diameter use

3. Find the circumference of the circle to the nearest tenth. Use 3
Find the circumference of the circle to the nearest tenth. Use 3.14 for .
EX1)
C = d
You know the diameter.
12 in.
C  3.14 (12)
Substitute for  and d.
C  37.68
Multiply.
EX2)
C = 2r
11 cm
C  2 (3.14)(11)
C  69.08

4. The circumference of a circle is 56.52, what is the diameter.
EX3)
The circumference of a circle is 56.52, what is the diameter.
Substitute
C = d
56.52 = 3.14 d
Divide 3.14 on both sides of equation
3.14
3.14
18 = d

5. The circumference of a circle is 50.24, what is the radius.
EX4)
The circumference of a circle is 50.24, what is the radius.
C = 2r
50.24 = 2(3.14)( r )
3.14
3.14
16 = 2r 2 2
8 = r

6. If the diameter or radius of a circle is a multiple of 7, use for p.
22 7
The diameter of a circular pond is 42 m. What is its circumference? Use
EX5)
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.

7. notes

8. Circumference of a Circle
Date _______________
Circumference of a Circle

9. Pi is approximately equal to ____ or .
Circumference -
For every circle, the ratio of circumference C to diameter d is the same. This ratio, , is the Greek letter , called pi. C d
Pi is approximately equal to ____ or .
To find Circumference knowing diameter
To find Circumference knowing radius
To find Diameter use

10. Find the circumference of the circle to the nearest tenth. Use 3
Find the circumference of the circle to the nearest tenth. Use 3.14 for .
EX1)
12 in.
EX2)
11 cm

11. EX3)
The circumference of a circle is 56.52, what is the diameter.

12. EX4)
The circumference of a circle is 50.24, what is the radius.

13. If the diameter or radius of a circle is a multiple of 7, use for p.
Helpful Hint
22 7
The diameter of a circular pond is 42 m. What is its circumference? Use
EX5)
for . 22 7