Giải thích các bước giải:
\(\begin{array}{l}
a.x \ge 0;x \ne \left\{ {4;9} \right\}\\
b.P = \frac{{2\sqrt x - 9 + \left( {2\sqrt x + 1} \right)\left( {\sqrt x - 2} \right) - \left( {\sqrt x + 3} \right)\left( {\sqrt x - 3} \right)}}{{\left( {\sqrt x - 3} \right).\left( {\sqrt x - 2} \right)}}\\
= \frac{{2\sqrt x - 9 + 2x - 3\sqrt x - 2 - x + 9}}{{\left( {\sqrt x - 3} \right).\left( {\sqrt x - 2} \right)}}\\
= \frac{{x - \sqrt x - 2}}{{\left( {\sqrt x - 3} \right).\left( {\sqrt x - 2} \right)}}\\
= \frac{{\left( {\sqrt x - 2} \right)\left( {\sqrt x + 1} \right)}}{{\left( {\sqrt x - 3} \right).\left( {\sqrt x - 2} \right)}}\\
= \frac{{\sqrt x + 1}}{{\sqrt x - 2}}\\
c.P \in Z\\
\to \frac{{\sqrt x + 1}}{{\sqrt x - 2}} \in Z\\
\to \frac{{\sqrt x - 2 + 3}}{{\sqrt x - 2}} = 1 + \frac{3}{{\sqrt x - 2}} \in Z\\
\to \sqrt x - 2 \in U\left( 3 \right)\\
\to \left[ \begin{array}{l}
\sqrt x - 2 = 3\\
\sqrt x - 2 = - 3\\
\sqrt x - 2 = 1\\
\sqrt x - 2 = - 1
\end{array} \right. \to \left[ \begin{array}{l}
x = 25\left( l \right)\\
\sqrt x = - 1\left( l \right)\\
x = 9\left( l \right)\\
x = 1\left( {TM} \right)
\end{array} \right.
\end{array}\)
