Recap:

This circle has a diameter of 1.

What is its circumference? 1

Recap.

This circle has a radius of r.

What is its circumference?

r

Approximating the Area of a Circle.

Imagine splitting a circle with radius r into 1 million triangles.

r

What can you tell me about the area of each triangle?

r

Each triangle is approximately ½ × base × radius

r

The base of the triangle is approximately :

Circumference 1 million

Why?

So the total area is:

1 million × ½ × × r

So the total area is: πr2

What is the area of this circle?

4