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8 points at extensions are concyclic - All-Russian MO 2002 Regional (R4) 8.6

Source:

September 17, 2024
geometryConcyclicsquare

Problem Statement

Each side of the convex quadrilateral was continued into both sides and on all eight extensions set aside equal segments. It turned out that the resulting 88 points are the outer ends of the construction the given segments are different and lie on the same circle. Prove that the original quadrilateral is a square.