Question 13
Find all functions $f: \mathbb{R} \to \mathbb{R}$ such that
$$
f(x + f(y)) - f(x) = (x + f(y))^3 - x^3
$$
for all $x, y \in \mathbb{R}$.
$$
f(x + f(y)) - f(x) = (x + f(y))^3 - x^3
$$
for all $x, y \in \mathbb{R}$.
MathNet 2011 Question 13
Math Olympiad Vault · MathNet 2011