If circle a has a radius of 13 inches, find the radian measure of arc BC. Arc BC has an angle of 81 degrees.
A formula that changes degrees to radians is: radians / pi = degrees / 180
---> radians / pi = 81 / 180
---> radians / pi = 0.45
multiplying by pi ---> radians = 0.45·pi
The radian measure of an arc is independent from the radius of the circle.
You would use the radius of the circle to find the length (in inches, centimeters, etc.) of the arc.