Rotation Equations've Got Me Stumped

[Krak1337]

I perfectly understand the simple yet inefficient rotation equations. Like to rotate on the z axis:

x=cos(°)*r
y=sin(°)*r

That's easy and all, but inefficient. If you rotate 89° on the z axis, when you then go to rotate on the y-axis, you have to re-calculate the radius again(which would end up being WAY smaller). But I don't get these equations which don't require any radius length for rotation:

x=cos(°)*x' - sin(°)*y'
y=sin(°)*x' + cos(°)*y'

As much as I've tried, I just don't get it. I fail to see how it works. Can someone please walk me through this? You might have to talk to me like I'm a 3-year-old for me to get it. :-\

[BlinkOk]

man i dont get that stuff either. i think it is really dependent on the timing of the rotations. ther's a tut over at kirupa you might wanna check out;
http://www.kirupa.com/developer/acti...tiple_axis.htm
there is a whole section on 3d there so make sure you check it all out.
hope this helps
blink