Ok, first things first. I'm a programmer, I'm actually working on a flash game and I'm always having a bad time trying to understand maths.

What I'm trying to create here is an archer autonomously firing on a target using the right angle. The problem is, I can't manage to get that angle. I've tried tons of stuff to no avail so I shall put this into a simple drawing.

I have two points, A and B. I have the distance, which is X as well as the curve, that forms a circle, this circle's diameter being Y. Now what I lack is, the angle between the line and the curve at point A (?).

Also, note that I'm not really good at maths, if at all. I may not understand complex terms and such.

Well this is it. Thanks to whoever solves this or tries solving it!

Also, if you need more information about my little problem just ask away as I'm aware that the info I gave may not be adequate.