MathDB

16

Part of 2009 Sharygin Geometry Olympiad

Problems(1)

prove an angle is right

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

5/31/2009
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.
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