obtuse-angled set, every triangle has one angle > 91^o
Source: BMO Shortlist 2015 G3 (UK)
September 27, 2018
geometrycombinatorial geometryangles
Problem Statement
A set of points of the plane is called obtuse-angled if every three of it's points are not collinear and every triangle with vertices inside the set has one angle . Is it correct that every finite obtuse-angled set can be extended to an infinite obtuse-angled set?(UK)