Arc length formula: n is the degree of the center angle, r is the radius, and α is the radian of the center angle. l=nπr÷180 or l=n/180·πr or l=|α|r

In a circle with radius R, since the length of the arc subtended by a central angle of 360° is equal to the circumference C=2πR, the length of the arc subtended by a central angle of n° is l=n°πR÷180°.

In the radian system, if the central angle of the arc is θ, then the formula L=Rθ. The formula for the area of ​​a sector is S=LR/2, and the corresponding formula for calculating the area of ​​a sector is S=RRθ/2.

In a circle, the line segment connecting the center of the circle and any point on the circle is called the radius of the circle. It is usually represented by the letter r.

The vertex of the central angle of a circle is at the center of the circle, and the angle where the two sides of the angle intersect the circumference is called the central angle of the circle. The value range of the central angle ∠AOB is 0°＜∠AOB＜360°