ta có : \(\dfrac{\sqrt{a}+a\sqrt{b}-\sqrt{b}-b\sqrt{a}}{ab-1}=\dfrac{a\sqrt{b}-b\sqrt{a}+\sqrt{a}-\sqrt{b}}{ab-1}\) \(=\dfrac{\sqrt{ab}\left(\sqrt{a}-\sqrt{b}\right)+\left(\sqrt{a}-\sqrt{b}\right)}{ab-1}=\dfrac{\left(\sqrt{ab}-1\right)\left(\sqrt{a}-\sqrt{b}\right)}{\left(\sqrt{ab}-1\right)\left(\sqrt{ab}+1\right)}\)