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.
Radians are the most useful angular measure in calculus because they allow derivative and integral identities to be written in simple terms, e.g.,
 |
for 
measured in radians.
Unless stated otherwise, all angular quantities considered in this work are assumed to be specified in radians.
