\[\begin{array}{l}
A = \frac{{4x}}{{\sqrt x - 3}}\,\,\,\,\\
DK:\,\,\,x \ge 0;\,\,\,x \ne 9.\\
\sqrt {A + 3} - \sqrt A = 1\,\,\,\,\,\,\,\,\left( {A \ge 0} \right)\\
\Leftrightarrow \sqrt {A + 3} = 1 + \sqrt A \\
\Leftrightarrow A + 3 = 1 + A + 2\sqrt A \\
\Leftrightarrow 2\sqrt A = 2\\
\Leftrightarrow \sqrt A = 1\\
\Leftrightarrow A = 1\\
\Leftrightarrow \frac{{4x}}{{\sqrt x - 3}}\, = 1\\
\Leftrightarrow 4x = \sqrt x - 3\\
\Leftrightarrow 4x - \sqrt x + 3 = 0\\
\Leftrightarrow pt\,\,\,VN.\\
Vay\,\,k\,\,\,co\,\,\,x\,\,\,thoa\,\,man.
\end{array}\]
