Đáp án:
$\begin{array}{l}
9)\sqrt {\dfrac{{17}}{4} - 3\sqrt 2 } \\
= \sqrt {\dfrac{{17 - 12\sqrt 2 }}{4}} \\
= \dfrac{{\sqrt {9 - 2.3.2\sqrt 2 + 8} }}{2}\\
= \dfrac{{\sqrt {{{\left( {3 - 2\sqrt 2 } \right)}^2}} }}{2}\\
= \dfrac{{3 - 2\sqrt 2 }}{2}\\
10)\sqrt {9 - 4\sqrt 5 } \\
= \sqrt {5 - 2.2.\sqrt 5 + 4} \\
= \sqrt {{{\left( {\sqrt 5 - 2} \right)}^2}} \\
= \sqrt 5 - 2
\end{array}$
