Sectors

A sector is a region of a circle bounded by a central angle and its intercepted arc .

The area of a sector is equal to the area of the circle multiplied by the ratio of the central angle to $360°$ .

For example, in the figure above, the area of the shaded sector is

$\begin{array}{l}\frac{50}{360}\cdot \pi r^2=\frac{5}{36}\pi \left(4\right)\\ =\frac{5}{9}\pi \text{square}\text{units}\end{array}$