Đáp án+Giải thích các bước giải:

`9:)` 

`sqrt(11-2sqrt30)`

`=sqrt((sqrt5)^2-2*sqrt5*sqrt6+(sqrt6)^2`

`=sqrt((sqrt5-sqrt6)^2)`

`=|sqrt5-sqrt6|`

`=sqrt6-sqrt5`

`10:)`

`sqrt(21-4sqrt17)`

`=sqrt((sqrt17)^2-2*sqrt17*2+2^2`

`=sqrt((sqrt17-2)^2)`

`=|sqrt17-2|`

`=sqrt17-2`

`11:)`

`sqrt(11-4sqrt7)`

`=sqrt((sqrt7)^2-2*sqrt7*2+2^2)`

`=sqrt((sqrt7-2)^2)`

`=|sqrt7-2|`

`=sqrt7-2`

`12:)`

`sqrt(11+2sqrt30)`

`=sqrt((sqrt5)^2+2*sqrt5*sqrt6+(sqrt6)^2`

`=sqrt((sqrt5+sqrt6)^2)`

`=|sqrt5+sqrt6|`

`=sqrt5+sqrt6`

$\begin{array}{c} \color{#60e6f0}{\texttt{#VN2010}} \end{array}$