Đáp án:
$1.D$
$2.C$
$3.B$
$4.D$
$5.D$
$6.A$
Giải thích các bước giải:
1) $x^2 = 16 \Rightarrow |x| = 4 \Rightarrow \left[\begin{array}{l}x = 4\\x = -4\end{array}\right.$
2) $\sqrt{8}.\sqrt{20}.\sqrt{4,9}$
$=2\sqrt{2}.\sqrt{2}.\sqrt{49}$
$= 2.2.7 = 28$
3) $\sqrt{5} - \sqrt{(2-\sqrt{5})^2}$
$= \sqrt{5} - |2 - \sqrt{5}|$
$= \sqrt{5} - (\sqrt{5} - 2)$
$= 2$
4) $\begin{cases}3x + 2 \geq 0\\(x -1)^2 > 0\end{cases}$
$\Leftrightarrow \begin{cases}x \geq -\dfrac{2}{3}\\x \ne 1\end{cases}$
5) $\dfrac{2}{\sqrt{3} - 1} - \sqrt{3}$
$= \dfrac{2(\sqrt{3} - 1)}{(\sqrt{3} - 1)(\sqrt{3} + 1)} - \sqrt{3}$
$= \sqrt{3} - 1 - \sqrt{3} = -1$
6) $\dfrac{1}{2 + \sqrt{3}} - \dfrac{1}{2 - \sqrt{3}}$
$= \dfrac{2 - \sqrt{3} - (2 + \sqrt{3})}{(2 -\sqrt{3})(2+\sqrt{3})} = -2\sqrt{3}$
