According to the definition of arc: an arc is the part between any two points on a circle. So the part between two points on the circumference is called an arc.

Arc length: the length of an arc passing through two points on the circle is called arc length.

Radian: an arc whose arc length is equal to the radius, and its central angle is 1 radian.

Extended data:

Arc length formula: arc length =nπr/ 180, where n is the number of angles, that is, the arc length corresponding to the central angle n.

But if we use radians, the above formula will become simpler: (note that radians are positive and negative)

L=|α| r, that is, the product of the size and radius of α.

Similarly, we can simplify the sector area formula:

S = | α| r 2/2 (the product of the size of α angle and the square of radius, from which we can see that when |α|=2π, that is, the fillet, the formula becomes S = π r 2, the formula of circular area! )