MathDB
Beautiful configurations

Source: 28th Iberoamerican Olympiad 2013, problem 6

September 25, 2013
rotationgeometrygeometric transformationcombinatorics proposedcombinatoricscombinatorial geometry

Problem Statement

A beautiful configuration of points is a set of nn colored points, such that if a triangle with vertices in the set has an angle of at least 120120 degrees, then exactly 2 of its vertices are colored with the same color. Determine the maximum possible value of nn.