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MathNet 2015-part-04 — 191 problems (EN–VI) Question 48

Math Olympiad Vault · MathNet 2015-part-04 — 191 problems (EN–VI)

Question 48

Let $ABC$ be a triangle and $\Gamma$ the circle with diameter $AB$. The bisectors of $\angle BAC$ and $\angle ABC$ intersect $\Gamma$ (also) at $D$ and $E$, respectively. The incircle of $ABC$ meets $BC$ and $AC$ at $F$ and $G$, respectively. Prove that $D, E, F$ and $G$ are collinear.