1. Circumference & Pi 
  3.14

2. Find the perimeter of the trapezoid. Find the area of the trapezoid9 6
17.5 5
Find the perimeter of the trapezoid.
Find the area of the trapezoid
A circle has a diameter of 30 feet. What is the radius?
The radius of a circle is 7 inches. What is the diameter?
30 feet
7 in

3. Circumference:
The distance around the outside of a circle
or think the perimeter of a circle
Pi (π):
The ratio of the circumference to diameter.

4. Circumference of a Circle
C = πd = 2πr π(d) = π(2r) = 2πr

5. π  3.14

6. Videos SAV Lesson 4 ~ Circumference:
Simple (pi = 3) :
Geeky:
Nerd exact pi:

7. Example 1a Find the circumference of the circle. Use 3.14 for π.
Write the circumference formula that uses diameter.
C = πd
Substitute the known values. C ≈ (3.14)(8)
Multiply C ≈ 25.12
The circumference of ⊙H is about mm.

8. Example 1b Find the circumference of the circle. Use 3.14 for π.
Write the circumference formula using the radius.
C = 2πr
Substitute the known values. C ≈ 2(3.14)(2.5)
Multiply. C ≈ 15.7
The circumference of ⊙J is about 15.7 feet.

9. Example 2 Natalya walked with her friend around a circular track.
The circumference of the track was meters. Find
the approximate length of the track’s radius. Use 3.14 for π.
Write the circumference formula C = 2πr
Substitute the known values ≈ 2(3.14)r
Multiply ≈ 6.28r
Divide by 6.28 on each side.
30 ≈ r
The radius of the track was approximately 30 m.

10. Use 3.14 for  in each problem.
Find the circumference of a circle with a diameter of 5 inches.
Find the circumference of a circle with a radius of 5 inches.
The circumference of a circle is mm.
What is the diameter?

11. Communication Prompt
Why do you think the word “circumference” is used instead of “perimeter” for the distance around a circle?
What is pi ()?