扇形指圆上被两条半径和半径所截之一段弧所围成的图形。因形状如一把扇子而得名。

扇形的圆心角∝面积∝弧长。

• 面积：
• 弧长：

α单位为α°(度)

如α单位为弧度「弪」

• 面积：
• 弧长：

A circular sector or circle sector (symbol: ⌔), is the portion of a disk enclosed by two radii and an arc, where the smaller area is known as the minor sector and the larger being the major sector. In the diagram, θ is the central angle in radians, the radius of the circle, and is the arc length of the minor sector.