Điều kiện: \(\left\{{}\begin{matrix}x>0\\x\ne9\end{matrix}\right.\)
\(A=\dfrac{\sqrt{x}\left(3-\sqrt{x}\right)+9+x}{\left(3-\sqrt{x}\right)\left(3+\sqrt{x}\right)}:\dfrac{-\left(3-\sqrt{x}\right)-\left(1+3\sqrt{x}\right)}{\sqrt{x}\left(3-\sqrt{x}\right)}\)
\(=\dfrac{3\sqrt{x}-x+9+x}{\left(3-\sqrt{x}\right)\left(3+\sqrt{x}\right)}:\dfrac{\sqrt{x}-3-1-3\sqrt{x}}{\sqrt{x}\left(3-\sqrt{x}\right)}\)
\(=\dfrac{9+3\sqrt{x}}{\left(3-\sqrt{x}\right)\left(3+\sqrt{x}\right)}:\dfrac{-4-2\sqrt{x}}{\sqrt{x}\left(3-\sqrt{x}\right)}\)
\(=\dfrac{-3\left(3+\sqrt{x}\right)}{\left(\sqrt{x}-3\right)\left(3+\sqrt{x}\right)}:\dfrac{2\left(2+\sqrt{x}\right)}{\sqrt{x}\left(\sqrt{x}-3\right)}\)
\(=\dfrac{-3\left(3+\sqrt{x}\right)}{\left(\sqrt{x}-3\right)\left(3+\sqrt{x}\right)}.\dfrac{\sqrt{x}\left(\sqrt{x}-3\right)}{2\left(2+\sqrt{x}\right)}\)
\(=\dfrac{-3\sqrt{x}}{2\left(2+\sqrt{x}\right)}\)
