MathDB
Determine angle A

Source: I.F.Sharygin contest 2009 - Correspondence round - Problem 5

May 31, 2009
geometrygeometric transformationreflectioncircumcirclegeometry proposed

Problem Statement

Given triangle ABC ABC. Point O O is the center of the excircle touching the side BC BC. Point O1 O_1 is the reflection of O O in BC BC. Determine angle A A if O1 O_1 lies on the circumcircle of ABC ABC.
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