Đáp án:
$\begin{array}{l}
b)B = \sqrt {3 - 2\sqrt 2 } + \sqrt {5 - 2\sqrt 6 } \\
= \sqrt {{{\left( {\sqrt 2 - 1} \right)}^2}} + \sqrt {{{\left( {\sqrt 3 - \sqrt 2 } \right)}^2}} \\
= \sqrt 2 - 1 + \sqrt 3 - \sqrt 2 \\
= \sqrt 3 - 1\\
c)C = m\sqrt {\dfrac{2}{{81{m^2}}}} \\
= m.\dfrac{{\sqrt 2 }}{{9\left| m \right|}}\\
= m.\dfrac{{\sqrt 2 }}{{ - 9m}}\left( {do:m < 0} \right)\\
= - \dfrac{{\sqrt 2 }}{9}\\
d)D = \sqrt {{x^2}{{\left( {x - 2} \right)}^2}} \\
= \left| x \right|.\left| {x - 2} \right|\\
= - x.\left( {2 - x} \right)\left( {do:x < 0} \right)\\
= {x^2} - 2x
\end{array}$
