I have a circle with $A$ as a center, $B$ and $C$ two points on the circle. I have the coordinates of $A$ (the center) and $B$ (the point on the circle). How can I find the coordinates of $C$ (another point on the circle knowing that $\angle BAC$ is $0.384$ rad (or $22^\circ$). The Y axis is upside down (see picture http://i.stack.imgur.com/4Vp4W.jpg)
So I have $(X_a, Y_a)$ and $(X_b, Y_b)$ and I need to find $(X_c, Y_c)$ respecting the given axis.