a.
thay x = 4 - \(\sqrt{2}\)
Ta có:
\(M=\dfrac{4}{4-\sqrt{2}-4}=\dfrac{4}{-\sqrt{2}}=-\dfrac{4}{\sqrt{2}}=-2\sqrt{2}\)
b.
\(\Leftrightarrow N=\dfrac{x+\sqrt{x}}{x-\sqrt{x}-2}-\dfrac{x-\sqrt{x}-2}{x-\sqrt{x}-2}\)
\(N=\dfrac{x+\sqrt{x}-x+\sqrt{x}+2}{x-\sqrt{x}-2}=\dfrac{2\sqrt{x}+2}{x-\sqrt{x}-2}=\dfrac{2\left(\sqrt{x}+1\right)}{x-2\sqrt{x}+\sqrt{x}-2}=\dfrac{2\left(\sqrt{x}+1\right)}{\sqrt{x}\left(\sqrt{x}-2\right)+\left(\sqrt{x}-2\right)}=\dfrac{2\left(\sqrt{x}+1\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)}=\dfrac{2}{\sqrt{x}-2}\)
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