Giải thích các bước giải:
\[\begin{array}{l}
D = \frac{2}{{\sqrt x - 3}}.Dk:\left\{ \begin{array}{l}
x \ne 9\\
x \ge 0
\end{array} \right.\\
a.D \in Z \Leftrightarrow \left( {\sqrt x - 3} \right) \in U(2) = \left\{ { \pm 1; \pm 2} \right\}\\
\Rightarrow x \in \left\{ {1;4;16;25} \right\}\\
b.D < \frac{1}{{\sqrt 2 }} \Leftrightarrow \frac{2}{{\sqrt x - 3}} < \frac{1}{{\sqrt 2 }} \Leftrightarrow \left\{ \begin{array}{l}
x \ge 0\\
\left[ \begin{array}{l}
\sqrt x - 3 < 0\\
\left\{ \begin{array}{l}
\sqrt x - 3 > 0\\
\sqrt x - 3 > 2\sqrt 2
\end{array} \right.
\end{array} \right.
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
0 \le x < 9\\
x > 17 + 12\sqrt 2
\end{array} \right.\\
\end{array}\]
