To find the circumference of a circle, use the formula 2

�
πr. This can also be written as
�
πD, since D = 2r.

To find the area of a circle, use the formula
�
πr
2
2
. It's important to remember to square the radius because area is always measured in square units.

A circle with a radius of 4 inches has an area of

A
4
�
π inches
2
2

B
16
�
π inches
2
2

C
8
�
π inches
2
2

D
2
�
π inches
2
2