Problem

Source: 2009 Oral Moscow Geometry Olympiad grades 10-11 p3

Tags: geometry, incenter, perpendicular, incircle



Altitudes $AA_1$ and $BB_1$ are drawn in the acute-angled triangle $ABC$. Prove that the perpendicular drawn from the touchpoint of the inscribed circle with the side $BC$, on the line $AC$ passes through the center of the inscribed circle of the triangle $A_1CB_1$. (V. Protasov)