Sign In
The radian measure of a central angle is defined as the quotient between the length of the arc intercepted by the angle and the radius of the circle.
Based on the diagram above, the radian measure of the central angle ∠ O is defined as follows.
θ=s/r
The arc length is proportional to the radius, so the radian measure θ of the central angle is a constant of proportionality. The radian measure is expressed in radians.