IMO Shortlist 2010 problem G3


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23. lipnja 2013.
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Let A_1A_2 \ldots A_n be a convex polygon. Point P inside this polygon is chosen so that its projections P_1, \ldots , P_n onto lines A_1A_2, \ldots , A_nA_1 respectively lie on the sides of the polygon. Prove that for arbitrary points X_1, \ldots , X_n on sides A_1A_2, \ldots , A_nA_1 respectively,
\max \left\{ \frac{X_1X_2}{P_1P_1}, \ldots, \frac{X_nX_1}{P_nP_1} \right\} \geq 1.

Proposed by Nairi Sedrakyan, Armenia
Izvor: Međunarodna matematička olimpijada, shortlist 2010