MathDB
prove an angle is right

Source: I.F.Sharygin contest 2009 - Correspondence round - Problem 16

May 31, 2009
geometry proposedgeometry

Problem Statement

Three lines passing through point O O form equal angles by pairs. Points A1 A_1, A2 A_2 on the first line and B1 B_1, B2 B_2 on the second line are such that the common point C1 C_1 of A1B1 A_1B_1 and A2B2 A_2B_2 lies on the third line. Let C2 C_2 be the common point of A1B2 A_1B_2 and A2B1 A_2B_1. Prove that angle C1OC2 C_1OC_2 is right.
Back to ProblemsView on AoPS