Radian Measure

Measure for the value of an angle. The radian measure of a plane angle indicates the length of the circular arc which is given by the associated angle field of the unit circle (see illustration).

 radian measure

The notation of the radian measure of an angle  is arc().

E.g. arc(360 degrees) = 2, arc(180 degrees) =  and in general for   = a degrees

               arc() = (a / 180) *  .