Problem

Source: Middle Europe Mathematical Olympiad 2009 TST Second day, Third problem

Tags: geometry, circumcircle, perpendicular bisector, geometry unsolved



It is given a convex quadrilateral $ ABCD$ in which $ \angle B+\angle C < 180^0$. Lines $ AB$ and $ CD$ intersect in point E. Prove that $ CD*CE=AC^2+AB*AE \leftrightarrow \angle B= \angle D$