Problem

Source: German TST, IMO ShortList 2003, combinatorics problem 3

Tags: geometry, combinatorial geometry, polygon, Extremal combinatorics, right angle, angles, IMO Shortlist



Let $n \geq 5$ be a given integer. Determine the greatest integer $k$ for which there exists a polygon with $n$ vertices (convex or not, with non-selfintersecting boundary) having $k$ internal right angles. Proposed by Juozas Juvencijus Macys, Lithuania


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