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IMO 2009 — Complete Shortlist Question 18

IMO Shortlist · IMO 2009 — Complete Shortlist

Question 18

Let $A B C$ be a triangle. The incircle of $A B C$ touches the sides $A B$ and $A C$ at the points $Z$ and $Y$, respectively. Let $G$ be the point where the lines $B Y$ and $C Z$ meet, and let $R$ and $S$ be points such that the two quadrilaterals $B C Y R$ and $B C S Z$ are parallelograms.
Prove that $G R=G S$.