Đáp án:
$\begin{array}{l}
f)\dfrac{{\sqrt {2{{\left( {\sqrt 2 - \sqrt 7 } \right)}^2}} }}{{\sqrt {56} - 4}}\\
= \dfrac{{\sqrt 2 .\left( {\sqrt 7 - \sqrt 2 } \right)}}{{2\sqrt {14} - 4}}\\
= \dfrac{{\sqrt 2 \left( {\sqrt 7 - \sqrt 2 } \right)}}{{2\sqrt 2 \left( {\sqrt 7 - \sqrt 2 } \right)}}\\
= \dfrac{1}{2}\\
g)\dfrac{{\left( {5\sqrt 2 + 2\sqrt 5 } \right)\left( {\sqrt 3 - 3\sqrt 2 } \right)}}{{\sqrt {30} }}\\
= \dfrac{{\sqrt {10} \left( {\sqrt 5 + \sqrt 2 } \right).\sqrt 3 \left( {1 - \sqrt 6 } \right)}}{{\sqrt {30} }}\\
= \left( {\sqrt 5 + \sqrt 2 } \right)\left( {1 - \sqrt 6 } \right)\\
= \sqrt 5 - \sqrt {30} + \sqrt 2 - 2\sqrt 3 \\
h)\dfrac{{10\sqrt {18} + 5\sqrt 3 - 15\sqrt {27} }}{{\sqrt 3 \left( {\sqrt 6 - 4} \right)}}\\
= \dfrac{{10.3\sqrt 2 + 5\sqrt 3 - 15.3\sqrt 3 }}{{3\sqrt 2 - 4\sqrt 3 }}\\
= \dfrac{{30\sqrt 2 - 40\sqrt 3 }}{{3\sqrt 2 - 4\sqrt 3 }}\\
= \dfrac{{10\left( {3\sqrt 2 - 4\sqrt 3 } \right)}}{{3\sqrt 2 - 4\sqrt 3 }}\\
= 10
\end{array}$
