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International Mathematical Olympiad 2000 — Official contest Question 6

IMO · International Mathematical Olympiad 2000 — Official contest

Question 6

Let $\overline{AH_1}$, $\overline{BH_2}$, and $\overline{CH_3}$ be the altitudes of an acute triangle $ABC$. The incircle $\omega$ of triangle $ABC$ touches the sides $BC$, $CA$ and $AB$ at $T_1$, $T_2$ and $T_3$, respectively. Consider the reflections of the lines $H_1H_2$, $H_2H_3$, and $H_3H_1$ with respect to the lines $T_1T_2$, $T_2T_3$, and $T_3T_1$. Prove that these images form a triangle whose vertices lie on $\omega$.