Area and volume > Area 2-D shapes
1234Area 2-D shapes

## Theory

You can find the area of a figure by dividing it into rectangles and half rectangles. This even works to find the (approximate) area of a circle. You know the area of a rectangle: .

It is handy to memorize the following area formulas:

By moving either point $P$ or point $Q$ parallel with the base the area does not change. This is called Cavalieri's principle.

The circumference of a circle with radius r is: .
The area of a circle with radius r is: $\mathrm{area}\left(\text{circle}\right)=\pi {r}^{2}$ .