1995 IMO Problems/Problem 5
Let be a convex hexagon with and , such that . Suppose and are points in the interior of the hexagon such that . Prove that .
Draw and to make equilateral and , and draw points and such that , , directed angle , and directed angle to make equilateral and . Notice that is on the circumcircle of and is on the circumcircle of . By Ptolemy, and . So, . Notice that octagon is symmetric about . So, .