MathDB
integer xy-net

Source: Romanian TST 1978, Day 2, P1

September 29, 2018
analytic geometrynumber theorycartesian plane

Problem Statement

Associate to any point (h,k) (h,k) in the integer net of the cartesian plane a real number ah,k a_{h,k} so that a_{h,k}=\frac{1}{4}\left( a_{h-1,k} +a_{h+1,k}+a_{h,k-1}+a_{h,k+1}\right) , \forall h,k\in\mathbb{Z} .
a) Prove that it´s possible that all the elements of the set A:={ah,kh,kZ} A:=\left\{ a_{h,k}\big| h,k\in\mathbb{Z}\right\} are different. b) If so, show that the set A A hasn´t any kind of boundary.