Olympiad Maths Prep

Track / Stage 6 / 247 of 400 #1247 of 2000

Problem 1247

National olympiad, first round
Number theory Difficulty 6.4 Prove it

23. Let Z[1]={α=a+b1:a,bZ},N(α)=a2+b2\boldsymbol{Z}[\sqrt{-1}]=\{\alpha=a+b \sqrt{-1}: a, b \in \boldsymbol{Z}\}, N(\alpha)=a^{2}+b^{2}.
(i) Introduce the concepts of divisibility, irreducible elements, and prime elements in Z[1]\boldsymbol{Z}[\sqrt{-1}], and establish the basic properties analogous to the first part of Chapter 1, Section 2.
(ii) Let α,βZ[1]\alpha, \beta \in \boldsymbol{Z}[\sqrt{-1}]. If αβ\alpha|\beta and βα\beta| \alpha hold simultaneously, then α,β\alpha, \beta are called associates. Prove that α,β\alpha, \beta are associates if and only if α=±β,±iβ\alpha= \pm \beta, \pm \mathrm{i} \beta.

This one wants a proof. Work it on paper, read the official solution, then mark yourself honestly — the ladder only means something if the record is true.

Official solution

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic, difficulty and ordering added by this site.