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IMO 2018 — Complete Shortlist Question 1

IMO Shortlist · IMO 2018 — Complete Shortlist

Question 1

Let $\mathbb{Q}_{\gt 0}$ denote the set of all positive rational numbers. Determine all functions $f: \mathbb{Q}_{\gt 0} \rightarrow \mathbb{Q}_{\gt 0}$ satisfying

$$
f\left(x^{2} f(y)^{2}\right)=f(x)^{2} f(y)
$$

for all $x, y \in \mathbb{Q}_{\gt 0}$.