Circumference & Area

Parts of a CircleParts of a Circle

diameter

radius

d = 2r

and

r = d2

1

Circumference(Distance around a circle)

C = d or C = 2 r

8 in.

C = 3.14(8)C = 25.12 in.

= 3.14

C = 2(3.14)(4)C = 25.12 in

4 in.

Give it a try!1. If the diameter is 10 feet, what is the

radius?

2. If the radius is 3.2 inches, what is the diameter?

3. Find the circumference:

4. Find the circumference:

15 cm

3 mm

Give it a try!1. If the diameter is 10 feet, what is the

radius? r = 5 feet2. If the radius is 3.2 inches, what is the

diameter? d = 6.4 in.3. Find the circumference:C = 3.14 x 15 = 47.1 cm

4.Find the circumference:C = 2 x 3.14 x 3 = 18.84 mm

15 cm

3 mm

Area of a Circle(The inside of the circle)

A = r A = r

2

3 m

A = 3.14(3 )A = 28.26 m

2

10 ind = 10 inr = 5 in

A = 3.14(5 )A = 78.5 in2

2 22

You try!

A = 2r

7 in 20 ft.

You try!

2

2

2

A = 2

rA = 3.14(7 )A = 153.86 in2

20 ft.

d = 20, so r = 10A = rA = 3.14(10 )A = 314 ft

2

7 in