radian is unit of length
The radian is a unit of angular measure defined such that an angle of one radian subtended from the center of a unit circle produces an arc with arc length 1. A full angle is therefore radians, so there are per radians, equal to or 57./radian. Similarly, a right angle is radians and a straight angle is radians. for measured in radians. Unless stated otherwise, all angular quantities considered in this work are assumed to be specified in radians.