MathDB
Putnam 2000 B6

Source:

September 6, 2011
Putnaminequalitiescollege contestscombinatoricscombinatorial geometryProbabilistic Method

Problem Statement

Let BB be a set of more than 2n+1n\tfrac{2^{n+1}}{n} distinct points with coordinates of the form (±1,±1,,±1)(\pm 1, \pm 1, \cdots, \pm 1) in nn-dimensional space with n3n \ge 3. Show that there are three distinct points in BB which are the vertices of an equilateral triangle.