MathDB
circle

Source: Canada 2005

June 26, 2009
geometrycircumcirclecombinatorics proposedcombinatorics

Problem Statement

Let SS be a set of n3n\ge 3 points in the interior of a circle. a)a) Show that there are three distinct points a,b,cSa,b,c\in S and three distinct points A,B,CA,B,C on the circle such that aa is (strictly) closer to AA than any other point in SS, bb is closer to BB than any other point in SS and cc is closer to CC than any other point in SS. b)b) Show that for no value of nn can four such points in SS (and corresponding points on the circle) be guaranteed.