Đáp án:
$A = \sqrt[]{125x}$
$ = \sqrt[]{25 . 5x}$
$ = 5\sqrt[]{5x}$
$B = \sqrt[]{80y^4}$
$ = \sqrt[]{16y^4 . 5}$
$ = 4y^2\sqrt[]{5}$
$C = \sqrt[]{5(1-\sqrt[]{2})^2}$
$ =(√2-1)\sqrt[]{5}$ (vì √2 > 1)
$D = \sqrt[]{27(2-√5)^2}$
$ = \sqrt[]{9.3(2-√5)^2}$
$= 3(√5-2)\sqrt[]{3}$ (vì √5 > 2)