Lời giải:
1.
\(M=\left[\frac{\sqrt{x}(\sqrt{x}-3)}{(\sqrt{x}-3)(\sqrt{x}+3)}-\frac{2x}{(\sqrt{x}-3)(\sqrt{x}+3)}\right].\frac{\sqrt{x}-3}{5-\sqrt{x}}\\ =\frac{-x-3\sqrt{x}}{(\sqrt{x}-3)(\sqrt{x}+3)}.\frac{\sqrt{x}-3}{5-\sqrt{x}}\\ =\frac{-\sqrt{x}(\sqrt{x}+3)}{(\sqrt{x}+3)(\sqrt{x}-3)}.\frac{\sqrt{x}-3}{5-\sqrt{x}}\\ =\frac{\sqrt{x}}{\sqrt{x}-5}\)
2.
$M=\frac{\sqrt{x}}{\sqrt{x}-5}=2$
$\Leftrightarrow \sqrt{x}=2(\sqrt{x}-5)$ ($x\neq 25$)
$\Leftrightarrow 10=\sqrt{x}$
$\Leftrightarrow x=100$ (tm)
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