So M and N are the midpoints of the bases AB and CD of the isosceles trapezoid ABCD. The bisectors of angles CAD and ACB intersect with MN at points P and Q respectively. K and L are on AC so that the angles QLC and AKP are 90 degree.

*Prove that the points K,L,M,N are on the same circle and if AD=c then find the radius of the circle.*

I think that LNK=LMK=90 degree and LK=c and is the radius of the circle.