`a)`\(M=\dfrac{1}{\sqrt{x}+2}+\dfrac{1}{2-\sqrt{x}}-\dfrac{3\sqrt{x}}{x-4}\); \(\left(x\ge0;x\ne4\right)\)
\(M=\dfrac{\left(\sqrt{x}-2\right)-\left(\sqrt{x}+2\right)-3\sqrt{x}}{\left(\sqrt{x}+2\right)\left(\sqrt{x}-2\right)}\)
\(M=\dfrac{\sqrt{x}-2-\sqrt{x}-2-3\sqrt{x}}{\left(\sqrt{x}+2\right)\left(\sqrt{x}-2\right)}\)
\(M=\dfrac{-3\sqrt{x}-4}{\left(\sqrt{x}+2\right)\left(\sqrt{x}-2\right)}\)
`b)`\(M\ge1\)
\(\Leftrightarrow\dfrac{-3\sqrt{x}-4}{\left(\sqrt{x}+2\right)\left(\sqrt{x}-2\right)}\ge1\)
\(\Leftrightarrow-3\sqrt{x}-4\ge x-4\)
\(\Leftrightarrow x+3\sqrt{x}\le0\)
\(\Leftrightarrow\sqrt{x}\left(\sqrt{x}+3\right)\le0\)
\(\Leftrightarrow x=0\) ( vì \(\sqrt{x}\ge0\) )
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