Đáp án:
$\begin{array}{l}
b)B = \sqrt {14 - 6\sqrt 5 } - \sqrt {9 + 4\sqrt 5 } - \sqrt {9 + 4\sqrt 5 } + 2\sqrt 5 \\
= \sqrt {9 - 2.3.\sqrt 5 + 5} - 2\sqrt {5 + 2.2\sqrt 5 + 4} + 2\sqrt 5 \\
= \sqrt {{{\left( {3 - \sqrt 5 } \right)}^2}} - 2\sqrt {{{\left( {\sqrt 5 + 2} \right)}^2}} + 2\sqrt 5 \\
= 3 - \sqrt 5 - 2\left( {\sqrt 5 + 2} \right) + 2\sqrt 5 \\
= 3 - \sqrt 5 - 2\sqrt 5 - 4 + 2\sqrt 5 \\
= - 1 - \sqrt 5
\end{array}$
