7: \(\dfrac{a}{2\sqrt{a}-1}=\dfrac{a\left(2\sqrt{a}+1\right)}{4a-1}\)
9: \(\dfrac{1}{\sqrt{a}+\sqrt{a+1}}=\dfrac{\sqrt{a+1}-\sqrt{a}}{a+1-a}=\sqrt{a+1}-\sqrt{a}\)
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