The formula of sector perimeter is: sector perimeter = sector radius ×2+ arc length, that is, c = 2r+(n÷360) π d = 2r+(n÷180) π r. The formula of sector area is S=(lR)/2? Or S=( 1/2)θR? .

R is the radius of the bottom circle, L is the arc length of the sector, and θ is the central angle.

Sector area = circle area * degree of central angle/360;

The circumference of the sector = diameter+the circumference of the sector * the degree of the central angle /360.

Brief introduction of fan

A figure surrounded by an arc and two radii passing through both ends of the arc is called a fan (the combination of a semicircle and a diameter is also a fan). Obviously, it is surrounded by a part of the circumference and its corresponding central angle. In Elements of Geometry, a sector is defined as a figure surrounded by two sides of an angle whose vertex is in the center of a circle and is cut into an arc by these two sides.