MathDB
2023 Putnam A4

Source:

December 3, 2023
PutnamPutnam 2023

Problem Statement

Let v1,,v12v_1, \ldots, v_{12} be unit vectors in R3\mathbb{R}^3 from the origin to the vertices of a regular icosahedron. Show that for every vector vR3v \in \mathbb{R}^3 and every ε>0\varepsilon>0, there exist integers a1,,a12a_1, \ldots, a_{12} such that a1v1++a12v12v<ε\left\|a_1 v_1+\cdots+a_{12} v_{12}-v\right\|<\varepsilon.