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MathNet 2019-part-01 — 184 problems (EN–VI) Question 28

Math Olympiad Vault · MathNet 2019-part-01 — 184 problems (EN–VI)

Question 28

We are given an arbitrary acute-angled triangle $ABC$ and its altitudes $AD$ and $BE$ where $D$ and $E$ denote their feet on sides $BC$ and $AC$, respectively. Let furthermore $F$ and $G$ be two points on segments $AD$ and $BE$, respectively, such that
$$
\frac{AF}{FD} = \frac{BG}{GE}.
$$
The line through $C$ and $F$ intersects $BE$ in point $H$ and the line through $C$ and $G$ intersects $AD$ in point $I$. Prove that the four points $F, G, H$ and $I$ are concyclic.