A geometry problem- i find it really hard to crack?

Let ABCD be a trapezium with parallel sides AB,CD such that AB>CD. Points K and L lie on the line segments AB and CD, respectively, so that AK/KB=DL/LC.Suppose that there are points P and Q on the line segment KL such that APB=BCD and CQD=ABC. Prove that the points P,Q,B and C are concyclic.try to use elementary math only. we have to prove for 2 cases