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Square of side 6 has 4 points at dist. 5 from each other in

Source: Romanian IMO Team Selection Test TST 2003, problem 11

August 17, 2003
geometrytrigonometrypigeonhole principlearea of a trianglegeometry solved

Problem Statement

In a square of side 6 the points A,B,C,DA,B,C,D are given such that the distance between any two of the four points is at least 5. Prove that A,B,C,DA,B,C,D form a convex quadrilateral and its area is greater than 21. Laurentiu Panaitopol