Radians and Degrees
In science and engineering, radians are much more convenient (and common) than degrees. A radian is defined as the angle between 2 radii (radiuses) of a circle where the arc between them has length of one radius.
Another way of putting it is: a radian is the angle subtended by an arc of length r (the radius).
One radian is about 57.3°.
Radians are especially useful in calculus where we want to interchange angles and other quantities (e.g. length). For example, radians are required in Fourier Series - and other areas (see my numerical methods manuals).
Most computer programs use radians as the default.
The expression to convert degrees to radians is: R= pi*D/180 where R is radians, D is degrees, and pi is 3.1416