IMO Shortlist 2015 problem G6
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Avg: 8,0Let be an acute triangle with . Let be its cirumcircle, its orthocenter, and the foot of the altitude from . Let be the midpoint of . Let be the point on such that and let be the point on such that . Assume that the points , , , and are all different and lie on in this order.
Prove that the circumcircles of triangles and are tangent to each other.
(Ukraine)
Izvor: https://www.imo-official.org/problems/IMO2015SL.pdf