A circle is a closed curve in a plane. All of its points are an equal distance from its center.

A circle is a closed curve in a plane. All of its points are an equal distance from its center.

A diameter is a line segment that has both of its endpoints on the circle and passes through the center.

A radius is the distance from the center to any point on the circle.

The circumference is the distance around a circle.

C d or 2C rC

d

or 2d r

2

dr or

2

Cr

If the circumference of the circle is 24 inches, what is its diameter?

Cd

24

3.14d

7.64d in

7.64d in

r = 8.5 m

If the radius of the circle is 8.5 meters, what is its circumference?

2C r 2 3.14 8.5C

53.38C m

If the circumference of the circle is 42 cm, what is its radius?

2

Cr

42

2(3.14)r

6.69r cm

6.69r cm

A sector is a portion of acircle enclosed by two radii and the arc which they intercept.

Base = ½ of the Circumference

= r

Hei

gh

t H

eig

ht

Height = radius

A = r²A = r²

Find the area of the circle if the radius is 2.5 centimeters.

2A r

23.14 2.5A

219.625A cm

r = 2.5 cm

Find the area of the circle if the diameter is 9 meters.

2A r

23.14 4.5A

263.585A m

d = 9 m

Find the area of the circle if the circumference is 28 feet.

2A r

23.14 4.46A

262.46A ft