Circle w with center O meets circle \Gamma at X, Y, and O is on \Gamma. Point Z \in \Gamma lies outside w such that X Z=11, O Z=15 and Y Z=13. If the radius of circle w is r, find r^{2}.
Circle w with center O meets circle \Gamma at X, Y, and O is on \Gamma. Point Z \in \Gamma lies outside w such that X Z=11, O Z=15 and Y Z=13. If the radius of circle w is r, find r^{2}.