Area and volume > Area 2-D shapes

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: $\mathrm{area}\left(\text{rectangle}\right)=\text{height}\cdot \text{width}$ .

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:
$\mathrm{circum}\left(\text{circle}\right)=2\pi r$ .

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