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PrintTeam Selection Test for EGMO 2024
Turkey 2024 geometry
Problem
Let be a triangle, be its circumcircle and be its incentre. Let the line meet at and at for the second time. The line meet at and at for the second time. Let the circumcircles of and meet at for the second time. Prove that the lines , , are concurrent.

Solution
Let . Since is the Miquel point of the quadrilateral we get that and are conicyclic. Therefore, we have and since we get that quadrilateral is cyclic. Similarly the quadrilateral is also cyclic. By using of the radical axis theorem on the circles , and we get the desired concurrency.
Techniques
Miquel pointRadical axis theoremAngle chasingTriangle centers: centroid, incenter, circumcenter, orthocenter, Euler line, nine-point circle