The quadrilateral ABCD is inscribed in a circle. The point P lies in the interior of ABCD, and ∠PAB=∠PBC=∠PCD=∠PDA. The lines AD and BC meet at Q, and the lines AB and CD meet at R. Prove that the lines PQ and PR form the same angle as the diagonals of ABCD. geometrycircumcirclepower of a pointradical axisgeometry proposed