a: \(M=\dfrac{3\sqrt{x}-9+x+9}{x-9}:\dfrac{2\sqrt{x}-5-\sqrt{x}+3}{\sqrt{x}\left(\sqrt{x}-3\right)}\)
\(=\dfrac{\sqrt{x}\left(\sqrt{x}+3\right)}{x-9}\cdot\dfrac{\sqrt{x}\left(\sqrt{x}-3\right)}{\sqrt{x}-2}=\dfrac{x}{\sqrt{x}-2}\)
b: Để M=9 thì \(x=9\sqrt{x}-18\)
\(\Leftrightarrow\left(\sqrt{x}-3\right)\left(\sqrt{x}-6\right)=0\)
=>x=9(loại) hoặc x=36(nhận)