\[\begin{array}{l}
\sqrt {4x - 20} + \sqrt {x - 5} - \frac{1}{3}\sqrt {9x - 45} = 4\\
DK:\,\,\,x \ge 5\\
Pt \Leftrightarrow \sqrt {4\left( {x - 5} \right)} + \sqrt {x - 5} - \frac{1}{3}\sqrt {9\left( {x - 5} \right)} = 4\\
\Leftrightarrow 2\sqrt {x - 5} + \sqrt {x - 5} - \sqrt {x - 5} = 4\\
\Leftrightarrow 2\sqrt {x - 5} = 4\\
\Leftrightarrow \sqrt {x - 5} = 2\\
\Leftrightarrow x - 5 = 4\\
\Leftrightarrow x = 9\,\,\,\left( {tm} \right).
\end{array}\]
