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KöMaL problem A, 2024

Geometry Difficulty 9.0 IMO level Prove it Hungary

Let triangle ABCABC be a given acute scalene triangle with altitudes BEBE and CFCF. Let DD be the point where the incircle of △ABC\triangle ABC touches side BCB C. The circumcircle of △BDE\triangle B D E meets line ABA B again at point KK, the circumcircle of △CDF\triangle C D F meets line ACA C again at point LL. The circumcircle of △BDE\triangle B D E and △CDF\triangle CDF meet line KLKL again at XX and YY, respectively. Prove that the incenter of △DXY\triangle DXY lies on the incircle of △ABC\triangle ABC.

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