a) \(P=\left(\dfrac{\sqrt{x}}{3+\sqrt{x}}+\dfrac{x+9}{9-x}\right):\left(\dfrac{3\sqrt{x}+1}{x-3\sqrt{x}}-\dfrac{1}{\sqrt{2}}\right)\)
ĐKXĐ : \(\left\{{}\begin{matrix}x\ge0\\9-x\ne0\\x-3\sqrt{x}\ne0\\\dfrac{3\sqrt{x}+1}{x-3\sqrt{x}}-\dfrac{1}{\sqrt{x}}\ne0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x\ge0\\x\ne9\\\sqrt{x}\left(\sqrt{x}-3\right)\ne0\\\sqrt{x}\left(3\sqrt{x}+1\right)-\left(x-3\sqrt{x}\right)\ne0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x\ge0\\x\ne9\\x\ne0\\2\sqrt{x}\left(\sqrt{x}+1\right)\ne0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x>0\\x\ne9\end{matrix}\right.\)
