I have a right triangle ABC. I know the measures of the opposite, hypoteneus, and adjacent sides.

Using this picture:

Image:Trigonometry triangle.svg - Wikipedia, the free encyclopedia

I want to find angle A.

I understand sin(A) = opposite / hypoteneus.

How do I find what A is though?

If I take arcsin(opposite/hypoteneus), it doesn't seem to give me the right answer (A).