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nonconvex quadrilaterals with fixed sum of distances

Source: VI All-Ukrainian Tournament of Young Mathematicians, Qualifying p1

May 25, 2021
geometryfixedconvexconvex quadrilateral3D geometryUkrainian TYM

Problem Statement

Find all nonconvex quadrilaterals in which the sum of the distances to the lines containing the sides is the same for any interior point. Try to generalize the result in the case of an arbitrary non-convex polygon, polyhedron.