a) đkxđ: \(\left\{{}\begin{matrix}\sqrt{x}-1\ne0\\x-1\ne0\\\frac{1}{\sqrt{x}+1}\ne0\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x\ne1\\x\ne-1\end{matrix}\right.\)
\(\left(\frac{1}{\sqrt{x}-1}-\frac{\sqrt{x}}{x-1}\right):\frac{1}{\sqrt{x}+1}\)
\(\Leftrightarrow\frac{1\left(\sqrt{x}+1\right)-\sqrt{x}}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}.\left(\sqrt{x}+1\right)\)
\(\Leftrightarrow\frac{1}{\sqrt{x}-1}\)
b) Để \(A< 0\Rightarrow\frac{1}{\sqrt{x}+1}< 0\)
\(\Rightarrow\sqrt{x}+1< 0\) ( do \(1>0\))
\(\Rightarrow\sqrt{x}< -1\)(vô lý)
=> k tìm dc x thỏa mãn