# What is the circumference and area of a circle with a diameter of 13 centimeters?

##### 2 Answers

Formula for circumference of a circle:

where,

r is the radius of the circle.

Formula for Area of a Circle:

The circumference is

The area is

#### Explanation:

Popular rational *approximations* for

So the circumference of our circle will be

The formula more commonly used is

The formula for the area of a circle is

In our case we have:

#"area" = pi r^2 = pi (13/2)^2 = pi (13^2/2^2) = pi (169/4) ~~ (355*169)/(113*4) = 59995 / 452 ~~ 132.73cm^2#

**Why is the area #pi r^2#?**

You can divide a circle of radius

This work better the more segments you have, but here's an illustration for just