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MathNet 2009-part-01 — 175 problems (EN–VI) Question 27

Math Olympiad Vault · MathNet 2009-part-01 — 175 problems (EN–VI)

Question 27

A $9 \times 12$ rectangle is divided into unit squares. The centers of all the unit squares, except the four corner squares and the eight squares adjacent (by side) to them, are colored red. Is it possible to numerate the red centers by $C_{1}, C_{2}, \ldots, C_{96}$ so that the following two conditions are fulfilled:
$1^{\circ}$ All segments $C_{1} C_{2}, C_{2} C_{3}, \ldots C_{95} C_{96}, C_{96} C_{1}$ have the length $\sqrt{13}$;
$2^{\circ}$ The polygonal line $C_{1} C_{2} \ldots C_{96} C_{1}$ is centrally symmetric?