a set of $n>2$ planar vectors
Source: All-Russian 2007
May 4, 2007
vectorinequalitiesgeometry unsolvedgeometry
Problem Statement
Given a set of planar vectors. A vector from this set is called long, if its length is not less than the length of the sum of other vectors in this set. Prove that if each vector is long, then the sum of all vectors equals to zero.
N. Agakhanov