Question 132
Find all functions $f: \mathbb{R} \to \mathbb{R}$ satisfying the equality
$$
f(f(x) + f(y)) = (x + y)f(x + y)
$$
for all real $x$ and $y$.
$$
f(f(x) + f(y)) = (x + y)f(x + y)
$$
for all real $x$ and $y$.
MathNet 2019-part-01 — 184 problems (EN–VI) Question 132
Math Olympiad Vault · MathNet 2019-part-01 — 184 problems (EN–VI)