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I can't do two fe :")

Source: INAMO 2015 Shortlist A6 ; INAMO 2015 Problem 04

December 30, 2018
algebrafunctional equationfunction

Problem Statement

Let functions f,g:R+R+f, g: \mathbb{R}^+ \to \mathbb{R}^+ satisfy the following: f(g(x)y+f(x))=(y+2015)f(x) f(g(x)y + f(x)) = (y+2015)f(x) for every x,yR+x,y \in \mathbb{R}^+. (a) Prove that g(x)=f(x)2015g(x) = \frac{f(x)}{2015} for every xR+.x \in \mathbb{R}^+. (b) State an example of function that satisfy the equation above and f(x),g(x)1f(x), g(x) \ge 1 for every xR+x \in \mathbb{R}^+.