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a set of $n>2$ planar vectors

Source: All-Russian 2007

May 4, 2007
vectorinequalitiesgeometry unsolvedgeometry

Problem Statement

Given a set of n>2n>2 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