Đáp án:
$\begin{array}{l}
Dkxd:x \ge 0;x\# 4\\
C = \left( {3 + \dfrac{{x - 2\sqrt x }}{{\sqrt x - 2}}} \right)\left( {3 + \dfrac{{x + 3\sqrt x }}{{3\sqrt x + 1}}} \right)\\
= \dfrac{{3\sqrt x - 6 + x - 2\sqrt x }}{{\sqrt x - 2}}.\dfrac{{9\sqrt x + 3 + x + 3\sqrt x }}{{3\sqrt x + 1}}\\
= \dfrac{{x + \sqrt x - 6}}{{\sqrt x - 2}}.\dfrac{{x + 12\sqrt x + 3}}{{3\sqrt x + 1}}\\
= \dfrac{{\left( {\sqrt x - 2} \right)\left( {\sqrt x + 3} \right)}}{{\sqrt x - 2}}.\dfrac{{x + 12\sqrt x + 3}}{{3\sqrt x + 1}}\\
= \dfrac{{\left( {\sqrt x + 3} \right)\left( {x + 12\sqrt x + 3} \right)}}{{3\sqrt x + 1}}
\end{array}$
