# Functional Inequality Proof

• Sep 6th 2011, 04:11 AM
strawberrysundae
Functional Inequality Proof
Let f: $\Re$ $\rightarrow$ $\Re$

be a real-valued function defined on the set of real numbers that satisfies:

$f(x+y)$ $yf(x)+f(f(x))$

for all real numbers $x$ and $y$. Prove that $f(x)=0$ for all $x$ $0$.
• Sep 6th 2011, 04:41 AM
FernandoRevilla
Re: Functional Inequality Proof
See problem 3 here:

2011 Imo Official Solutions