• Circumference:C = πdC = 2πr

• Area:A = πr2

1-5 Formulas of Circles

• Find the circumference and area.

d = 12 in

Example

C = 2πrC = 2π(6)C = 12π = 37.7

A = πr2

A = π(6)2

A = 36π = 113.1

• The circumference of a circle is 24π, what is the area?

• The area of a circle is 28.27, what is the diameter?

Example

C = 2πr24π = 2πr A = πr2

24 = 2r A = π(12)2

12 = r A = 144π = 452.4

A = πr2

28.27 = πr2

9 = r2

3 = r d = 6

Example

Find the area of the shaded region.

3

Square CircleA = lw A = πr2 A = 6 x 6 A = π(3)2

A = 36 A = 9π = 28.27

Shaded RegionA = Square – CircleA = 36 – 28.27A = 7.73