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Japan mathematical olympiad finals 2006, problem 1

Source:

March 3, 2006
trigonometrygeometry proposedgeometry

Problem Statement

Given five distinct points A,M,B,C,DA,M,B,C,D in this order on the circumference of the circle OO such that MA=MB.MA=MB. Let P,QP,Q be the intersection points of the line ACAC and MDMD, and that of the line BDBD and MC,MC, respectively. If two intersection points of the line PQPQ and the circumference of the circle OO are X, Y,X,\ Y, then prove that MX=MY.MX=MY.