Function sectorA

sectorA(r: number, rad: number): number
Calculates the area of a sector of a circle.
Parameters
- r: number
  The radius
- rad: number
  The spanned radians
Returns number
Example
```
// Returns 39.26990816987242
const area = Chalkboard.geom.sectorA(5, Chalkboard.PI());
```
- Defined in Chalkboard.geom.ts:379