Finding third point of right triangle 
I have the length of BC,and AC and the coordinates of points A and C. I'm trying to find the coordinates of B.

I believe you can find the length of $AB$ (Pythagoras!). If you let the coordinates of $B$ be $(x,y),$ then since you know the other distances and coordinates, you can use the distance formula to find two equations in $x$ and $y$ (apply it to $|BA|$ and $|BC|$ in turn) that you can hopefully solve for $(x,y).$
