How do you find the length of an arc in a circle?

To calculate the length of an arc in the circle you need
to measure the radius (r ), and the central angle (a)

The
central angle is the angle subtended at the center of a circle by two given points on
the circle.

or, the central angle is the ratio of the arc
to the radius.

The length of the arc = radius X central
angle

                  or s= r *
a

Example: in a circle whose radius is 10 cm, and the
central angle is 4/5 ... find the length of the arc

    s =
r * a = 10 * 4/5 = 8 cm