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MathNet 2007-part-03 — 185 problems (EN–VI) Question 50

Math Olympiad Vault · MathNet 2007-part-03 — 185 problems (EN–VI)

Question 50

Let $f: \mathbb{R}^+ \to \mathbb{R}^+$ be a function satisfying
$$
(f(xy))^2 = f(x^2)f(y^2)
$$
for all $x, y \in \mathbb{R}^+$ with $x^2y^3 \gt 2008$.
Prove that $(f(xy))^2 = f(x^2)f(y^2)$ for all $x, y \in \mathbb{R}^+$.