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IMO Team Selection Contest I

Estonia geometry

Problem

Let be a triangle with and let be its incenter. The line meets at , and the line through perpendicular to meets at . Prove that the reflection of in lies on the circumcircle of triangle .
Solution
Solution. See IMO 2016 shortlist, problem G4.

Techniques

Triangle centers: centroid, incenter, circumcenter, orthocenter, Euler line, nine-point circleCyclic quadrilateralsAngle chasing