I'm wondering if there exists a non trivial set of pairs of irrationals that gives a rational when multiplied together. What I mean with trivial is for instance the set of pairs composed of an irrational and one of its multiplicative inverse : $\{(x,r/x) \ | \ x \in \mathbb{R} \setminus \mathbb{Q} \text{ and } r \in \mathbb{Q}^*\}$.
For instance let $K_{\sqrt{3}}=\{x \in \mathbb{R} \setminus \mathbb{Q} \ | \ x\sqrt{3} \in \mathbb{Q} \} $. We know that the rational multiplicatives of $\sqrt{3}$ belong to $K_{\sqrt{3}}$. Is there anything else ?
Of course any pair of irrational numbers whose product is rational is necessarily of the trivial form you mention.
That's just because if $xy=r\in\mathbb Q$, then $y=r/x$ and the pair is $(x,r/x)$ (we assume $r\neq 0$).