Đáp án:
$\begin{array}{l}
Dkxd:x \ge 0;x \ne 4\\
Do:\sqrt x \ge 0\\
\Rightarrow \sqrt x - 2 \ge - 2\\
\Rightarrow \dfrac{1}{{\sqrt x - 2}} \le \dfrac{{ - 1}}{2}\\
\Rightarrow \dfrac{3}{{\sqrt x - 2}} \le \dfrac{{ - 3}}{2}\\
\Rightarrow GTLN:\dfrac{3}{{\sqrt x - 2}}\,\text{là}:\dfrac{{ - 3}}{2}\\
\text{Dấu = xảy ra khi}:x = 0
\end{array}$