a. $\sqrt{(\sqrt 2 -1)^2}\\ =\Big|\Big. \sqrt 2-1\Big|\Big.\\ = \sqrt 2-1 $ (vì $\sqrt2 > 1$)
b. $\sqrt{(\sqrt 2 -5)^2}\\ =\Big|\Big. \sqrt 2-5\Big|\Big.\\ = 5-\sqrt 2 $ (vì $5>\sqrt2 $)
c. $\sqrt{(3-\sqrt 5 )^2}\\ =\Big|\Big. 3-\sqrt 5\Big|\Big.\\ = 3-\sqrt 5 $ (vì $3>\sqrt 5 $)
d. $\sqrt{(2+\sqrt 3 )^2}+\sqrt{(2-\sqrt 3 )^2}\\ =\Big|\Big. 2+\sqrt 3\Big|\Big.+\Big|\Big. 2-\sqrt 3\Big|\Big.\\ =2+\sqrt 3+ 2-\sqrt 3 = 4 $ (vì $2>\sqrt 3 $)