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Regional Olympiad - Republic of Srpska 2004 Grade 9 Problem 3

Source: Regional Olympiad - Republic of Srpska 2004

September 19, 2018
geometryisoscelesangles

Problem Statement

Let ABCABC be an isosceles triangle with A=B=80\angle A=\angle B=80^\circ. A straight line passes through BB and through the circumcenter of the triangle and intersects the side ACAC at DD. Prove that AB=CDAB=CD.