MathDB
(x-y) /(1 +xy )<1, for 2 of 3 positive numbers

Source: Portugal OPM 1996 p2

May 18, 2024
algebrainequalities

Problem Statement

Prove that given three positive numbers, we can choose two of them, say xx and y,y, with x>yx >y such that xy1+xy<1.\frac{x-y}{1 +xy }<1. Prove also that if the number 11 that appears in the second member of the previous inequality is replaced by a lower number, even if very close to 11, the previous proposition is false.