Đáp án:
$\begin{array}{l}
a)\dfrac{3}{{\sqrt 7 - 2}} + \sqrt {{{\left( {\sqrt 7 - 3} \right)}^2}} \\
= \dfrac{{3\left( {\sqrt 7 + 2} \right)}}{{7 - {2^2}}} + \left| {\sqrt 7 - 3} \right|\\
= \dfrac{{3\left( {\sqrt 7 + 2} \right)}}{{7 - 4}} + 3 - \sqrt 7 \\
= \sqrt 7 + 2 + 3 - \sqrt 7 \\
= 5\\
b)\left( {\dfrac{{\sqrt x }}{{\sqrt x - 1}} - \dfrac{x}{{x - \sqrt x }}} \right):\dfrac{{\sqrt x + 1}}{{x - 1}}\\
= \left( {\dfrac{{\sqrt x }}{{\sqrt x - 1}} - \dfrac{x}{{\sqrt x \left( {\sqrt x - 1} \right)}}} \right):\dfrac{1}{{\sqrt x - 1}}\\
= \left( {\dfrac{{\sqrt x }}{{\sqrt x - 1}} - \dfrac{{\sqrt x }}{{\sqrt x - 1}}} \right).\left( {\sqrt x - 1} \right)\\
= 0.\left( {\sqrt x - 1} \right)\\
= 0
\end{array}$
