\(\dfrac{1}{\sqrt{a}-1}-\dfrac{1}{\sqrt{a}}\)
\(=\dfrac{\sqrt{a}}{\sqrt{a}.\left(\sqrt{a}-1\right)}-\dfrac{\sqrt{a}-1}{\sqrt{a}.\left(\sqrt{a}-1\right)}\)
\(=\dfrac{\sqrt{a}-\sqrt{a}+1}{a-\sqrt{a}}\)
\(=\dfrac{1}{a-\sqrt{a}}\)
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