m: Ta có: \(M=\dfrac{1}{\sqrt{x}+3}+\dfrac{1}{\sqrt{x}-3}-\dfrac{6}{x-9}\)
\(=\dfrac{\sqrt{x}-3+\sqrt{x}+3-6}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\)
\(=\dfrac{2}{\sqrt{x}+3}\)
\(M=\dfrac{\sqrt{x}-3+\sqrt{x}+3-6}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}=\dfrac{2\sqrt{x}-6}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}\)
\(=\dfrac{2\left(\sqrt{x}-3\right)}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)}=\dfrac{2}{\sqrt{x}+3}\)
\(A=\dfrac{\sqrt{x}+1-\sqrt{x}+3}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-3\right)}.\dfrac{\sqrt{x}\left(\sqrt{x}-3\right)}{\sqrt{x}}\)
\(=\dfrac{4}{\sqrt{x}+1}\)
\(A=\dfrac{4\sqrt{x}-1-x-2\sqrt{x}+x-2\sqrt{x}}{x-4}.\dfrac{x-4}{3}\)
\(=-\dfrac{1}{3}\)
