Problem

Source: 2009 Sharygin Geometry Olympiad Final Round problem 7 grade 10

Tags: geometry, vector, Integer



Given points $O, A_1, A_2, ..., A_n$ on the plane. For any two of these points the square of distance between them is natural number. Prove that there exist two vectors $\vec{x}$ and $\vec{y}$, such that for any point $A_i$, $\vec{OA_i }= k\vec{x}+l \vec{y}$, where $k$ and $l$ are some integer numbers. (A.Glazyrin)