MathDB
vector w = (a, b, c) such that a^2 + b^2 + c^2<= 48

Source: Austrian - Polish 1995 APMC

May 3, 2020
vectorinequalitiesSumminalgebra

Problem Statement

Consider the cube with the vertices at the points (±1,±1,±1)(\pm 1, \pm 1, \pm 1). Let V1,...,V95V_1,...,V_{95} be arbitrary points within this cube. Denote vi=OViv_i = \overrightarrow{OV_i}, where O=(0,0,0)O = (0,0,0) is the origin. Consider the 2952^{95} vectors of the form s1v1+s2v2+...+s95v95s_1v_1 + s_2v_2 +...+ s_{95}v_{95}, where si=±1s_i = \pm 1. (a) If d=48d = 48, prove that among these vectors there is a vector w=(a,b,c)w = (a, b, c) such that a2+b2+c248a^2 + b^2 + c^2 \le 48. (b) Find a smaller dd (the smaller, the better) with the same property.