Algebra · Algebraic identities · Reciprocals · Constructive procedure

Problem 1, 2015

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RegionalProof

A positive real number \(x\) is written on a board. In one move you are allowed to do the following: if a number \(a\) is already on the board, you may write down one of the numbers \(a+1\) or \(\frac{1}{a}\); and if numbers \(a\) and \(b\) with \(a > b\) are already on the board, you may write down one of the numbers \(a+b\) or \(a-b\).

Prove that after finitely many moves it is possible to have the number \(x^2\) on the board.

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Serbian Regional Competition (Okruzno takmicenje) 2015, high school grade I, category A, problem 1. Organized by the Mathematical Society of Serbia (DMS). Source