Areas of Sector and Segment of Circle
* Circumference of a circle of radius r is 2πr
* Area of circle is πr².
* Length of the arc of a sector of a angle θ is \frac{θ}{360} × 2πr
* Area of a sector of angle θ is \frac{θ}{360} × πr²
* Area of a segment is the area of corresponding sector minus the area of the corresponding triangle.
* Areas of combinations of plane figures
* A collection of points that are on a plane is known as plane figure.