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Prove that f(x) lies in [0,1]

Source: All Russian 2014 Grade 10 Day 1 P2

May 3, 2014
functionalgebraRussiaFunctional inequality

Problem Statement

Given a function f ⁣:RRf\colon \mathbb{R}\rightarrow \mathbb{R} with f(x)2f(y)f(x)^2\le f(y) for all x,yRx,y\in\mathbb{R} , x>yx>y, prove that f(x)[0,1]f(x)\in [0,1] for all xRx\in \mathbb{R}.