7 vertices of a 27-gon, among 3 form isosceles or 4 isosceles trapezoid
Source: Germany Federal - Bundeswettbewerb Mathematik 2012, round 1, p4
April 11, 2020
combinatorial geometryregular polygonisoscelestrapezoidIsosceles Trianglecombinatoricsgeometry
Problem Statement
From the vertices of a regular 27-gon, seven are chosen arbitrarily. Prove that among these seven points there are three points that form an isosceles triangle or four points that form an isosceles trapezoid.