a) Ta có: \(A=\dfrac{1}{\sqrt{x}-x}:\left(\dfrac{1}{1-\sqrt{x}}+\dfrac{\sqrt{x}}{1-\sqrt{x}+x}\right)\)
\(=\dfrac{1}{\sqrt{x}\left(1-\sqrt{x}\right)}:\left(\dfrac{1-\sqrt{x}+x+\sqrt{x}\left(1-\sqrt{x}\right)}{\left(1-\sqrt{x}\right)\left(1-\sqrt{x}+x\right)}\right)\)
\(=\dfrac{1}{\sqrt{x}\left(1-\sqrt{x}\right)}:\dfrac{x-\sqrt{x}+1+\sqrt{x}-x}{\left(1-\sqrt{x}\right)\left(x-\sqrt{x}+1\right)}\)
\(=\dfrac{1}{\sqrt{x}\left(1-\sqrt{x}\right)}\cdot\dfrac{\left(1-\sqrt{x}\right)\left(x-\sqrt{x}+1\right)}{1}\)
\(=\dfrac{x-\sqrt{x}+1}{\sqrt{x}}\)
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