L=πRα/ 180 If α is in radians, L=Rα.

So S=R? α/2=RL/2

Sector area S= arc length L× radius /2

Deduction process: S=πR? ×L/2πR=LR/2 or S=nπR? /360=(nπR/ 180)/2×r

Components of the department:

1. The part between point A and point B on the circle is simply called "arc" and is pronounced as "arc AB" or "arc AB".

2. The angle with the center of the circle as the center point is called the "central angle".

3. A statistical chart is a "fan chart".

The area of the circle is πr2. The area of the sector can be multiplied by the area of the circle by the ratio of radian angle and 2π (because the area of the sector is proportional to its angle, and 2π is the angle of the whole circle);

If l is used to represent the arc length of the sector, a can be multiplied by the total area and divided by 2πr: