The reason you suck at math is that you want to memorize the functions. Understand how it works from the ground up, and you will never have to memorize a thing. If you can draw a right triangle with angles A, B, C and edge lengths a, b, c, and if you can express "sin(A)" or "cos(B)" in terms of a, b or c, then you can easily solve just about any problem, and derive just about any trig inequality.

It takes practice at first, but trust me: Memorization is the dumbest way to do math. I know, I've seen people do it.