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).
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) *
.