Circumference & Pi 3.14. Find the perimeter of the trapezoid. Find the area of the trapezoid A circle has a diameter of 30 feet. What is the.

Circumference & Pi

3.14

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?

96

9

17.5

5

30 feet

7 in

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.

C = πd = 2πr

π(d) = π(2r)

= 2πr

Circumference of a Circle

π 3.14

Videos

SAV Lesson 4 ~ Circumference:

Simple (pi = 3) : http://www.onlinemathlearning.com/circle-circumference.html

Geeky: http://www.youtube.com/watch?v=ORN7qLkuKOk&NR=1

Nerd exact pi: http://www.youtube.com/watch?v=cuhSPfyuulM&NR=1

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 25.12 ⊙ mm.

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.⊙

Natalya walked with her friend around a circular track. The circumference of the track was 188.4 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. 188.4 ≈ 2(3.14)r Multiply. 188.4 ≈ 6.28r Divide by 6.28 on each side.

30 ≈ r

The radius of the track was approximately 30 m.

28.6

28.6

28.6

4.188 r

Use 3.14 for in each problem.

1. Find the circumference of a circle with a diameter of 5 inches.

2. Find the circumference of a circle with a radius of 5 inches.

3. The circumference of a circle is 39.25 mm. What is the diameter?

Why do you think the word “circumference” is used instead of “perimeter” for the distance around a circle?

What is pi ()?