Question 17
In the diagram below, $AB$ is a diameter of the circle with centre $O$, $MN$ is a chord of the circle that intersects $AB$ at $P$, $\angle BON$ and $\angle MOA$ are acute angles, $\angle MPA=45^\circ$, $MP=\sqrt{56}$, and $NP=12$. Find the radius of the circle.
