Circle: Area

How to find the area of a circle: formula, 2 examples, and their solutions.

Formula

Formula

A = πr2

A: Area of a circle
r: Radius

Example 1

Example

Solution

r = 5

A = π⋅52

52 = 25

So π⋅52 = 25π.

So the area of the given circle is 25π.

Example 2

Example

Solution

The diameter is 13.

So the radius is the half of the diameter:
13/2.

r = 13/2

A = π⋅[13/2]2

[13/2]2 = 132/22

Power of a Quotient

So π⋅[13/2]2 = [132/22]π.

132 = 169
22 = 4

So [132/22]π = [169/4]π.

So [169/4]π is the answer.