Question 3
In the quadrilateral $PQRS$, $A$, $B$, $C$ and $D$ are the midpoints of the sides $PQ$, $QR$, $RS$ and $SP$ respectively, and $M$ is the midpoint of $CD$. Suppose $H$ is the point on the line $AM$ such that $HC=BC$. Prove that $\angle BHM=90^\circ$.