Shoulder located in the middle (top) instead of corner. Inverse Kinematic

[piraky]

There are many inverse Kinematic equations for 2D arm located in the corner.
Our group decided to mount the shoulder on the top, in the middle at (x/2, 0).
Can anyone give me the equations that converts x,y coordinates(set up like on the screen) to two angles?
I want to have the arm bent only in one way, so that the elbow joint will not flip from theta to negative theta.

Thank you!