a)\(=\dfrac{\left(\sqrt{m}-\sqrt{n}\right)\sqrt{mn}}{\left(\sqrt{m}-\sqrt{n}\right)\left(\sqrt{m}+\sqrt{n}\right)}=\dfrac{\sqrt{mn}}{\sqrt{m}+\sqrt{n}}\)
b)\(=\dfrac{a^2\sqrt{b}-b\sqrt{ab}}{ab\sqrt{a}-b^2}=\dfrac{\sqrt{ab}\left(a\sqrt{a}-b\right)}{b\left(a\sqrt{a}-b\right)}=\dfrac{\sqrt{a}}{\sqrt{b}}\)
c)\(=\dfrac{\left(a-\sqrt{2}\right)\left(a+\sqrt{2}a+2\right)}{a-\sqrt{2}}=a+\sqrt{2}a+2\)
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