coloring vertices of nonagon using 2 colors
Source: 1993 German Federal - Bundeswettbewerb Mathematik - BWM - Round 1 p1
November 20, 2022
combinatoricscombinatorial geometryColoring
Problem Statement
In a regular nonagon, each vertex is colored either red or green. Three corners of the nonagon determine a triangle. Such a triangle is called red or green if all its vertices are red or green if all are green. Prove that for each such coloring of the nonagon there are at least two different ones , that are congruent triangles of the same color.