Let A1,B1,C1 be the feet of altitudes of an acute-angled triangle ABC. The incircle of triangle A1B1C1 touches A1B1,A1C1,B1C1 at points C2,B2,A2 respectively. Prove that the lines AA2,BB2,CC2 concur at a point lying on the Euler line of triangle ABC. geometrymittenpunktconcurrencySharygin Geometry OlympiadSharygin 2023