MathDB
Colouring problem

Source:

October 24, 2020
combinatoricsgraphing linesColoring

Problem Statement

Let n,kn,k be integers such that nk3n\geq k\geq3. Consider n+1n+1 points in a plane (there is no three collinear points) and kk different colors, then, we color all the segments that connect every two points. We say that an angle is good if its vertex is one of the initial set, and its two sides aren't the same color. Show that there exist a coloration such that the \\ total number of good angles is greater than n(k2)(nk)2n \binom{k}{2} \lfloor(\frac{n}{k})\rfloor^2