Thats a hell of a question. It is such a complex question deep down but on the surface for us programmers.
(In degrees) sin(angle) = cos(angle+90)
(in radians) sin(angle) = cos(angle+PI/2)
In other words you can _always_ use a sin when you were going to use a cos. They have the same shape, input and output range. They are, for our purposes, the same thing. One day Ill get desperate enough to replace all my calls ot cos with calls to sin to save bytes ;-)