Question 97
Find all functions $f: [0, +\infty) \to [0, +\infty)$, which for all non-negative $x, y$ satisfy the equality:
$$
f(f(x) + f(y)) = xyf(x + y).
$$
$$
f(f(x) + f(y)) = xyf(x + y).
$$
MathNet 2018-part-06 — 181 problems (EN–VI) Question 97
Math Olympiad Vault · MathNet 2018-part-06 — 181 problems (EN–VI)