# Applying pi

## Circumference

Using only this photo, could you find the circumference of this ferris wheel to within a few feet?

First we could take the height of a person who looks to be around 6 feet and figure out the radius of the circle:

5 * 6 = roughly 30 feet

With the radius we can use

**π**to determine the**circumference**directly:We correctly find that it’s approximately 188 feet around the perimeter of the wheel, all thanks to π!

## Area

How can we estimate the area of any circle given its radius?

Let’s approximate the answer using a pizza slice analogy.

**Below is an interactive illustration;**click the arrows to change the number of slices in the pie:As we increase n, the perimeter of the pizza approaches the circumference of the circle. As we increase the number of slices:

- the height of the slice approaches the radius of the circle (
**h = r**) - the area of the pizza approaches the area of the circle (
**area of pizza = area of circle**)

This leads to a well-known equation which relates the area and radius of any circle: