IMO Shortlist 2003 problem A5


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2. travnja 2012.
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Let \mathbb{R}^+ be the set of all positive real numbers. Find all functions f: \mathbb{R}^+ \longrightarrow \mathbb{R}^+ that satisfy the following conditions:

- f(xyz)+f(x)+f(y)+f(z)=f(\sqrt{xy})f(\sqrt{yz})f(\sqrt{zx}) for all x,y,z\in\mathbb{R}^+;

- f(x)<f(y) for all 1\le x<y.
Izvor: Međunarodna matematička olimpijada, shortlist 2003