If you draw a circle with parametric:

x = cos(T)

y = sin(T)

You'll get a circle movement. If you divide the circle into 4 equal pieces and name the point (1,0) 0, you go round a quarter of a circle against the clock (I mean not-clockwise

)(which makes 0,5pi), the sin is max, which equals 1. And when you add another quarter, you get at the point of 1pi, where sin is min, which equals 0. So every time you get

0 + k x pi, the sin equals 0, the cos equals 1, and everytime you get 0,5 + k x pi, the sin equals 1 and the cos equals 0. The way blah54 does it, might even be better, but that's personal.

Man, don't we all love math