Sử dụng tính chất $\sqrt{A^2}=|A|=\left\{ \begin{array}{l} A(A\ge0) \\ -A(A<0)\end{array} \right .$
1) $=|2+\sqrt5|-|2-\sqrt5|$
$=2+\sqrt5-(\sqrt5-2)$
$=4$
3) $=|\sqrt2+1|-|1-\sqrt2|$
$=(\sqrt 2+1)-(\sqrt2-1)$
$=2$
5) $=\sqrt{(\sqrt3)^2-2\sqrt3+1}+\sqrt{(\sqrt3)^2+2\sqrt3+1}$
$=\sqrt{(\sqrt3-1)^2}+\sqrt{(\sqrt3+1)^2}$
$=|\sqrt3-1|+|\sqrt3+1|$
$=(\sqrt3-1)+(\sqrt3+1)$
$=2\sqrt3$
7) $=\sqrt{(\sqrt5)^2+2\sqrt5+1}+\sqrt{(\sqrt5)^2-2\sqrt5+1}$
$=\sqrt{(\sqrt5+1)^2}+\sqrt{(\sqrt5-1)^2}$
$=|\sqrt5+1|+|\sqrt5-1|$
$=(\sqrt5+1)+(\sqrt5-1)$
$=2\sqrt5$
