Hướng dẫn giải:
a. $\sqrt{(2-\sqrt{3})^{2}}=\left | 2-\sqrt{3} \right |=2-\sqrt{3}$
Vì $2=\sqrt{4}, \sqrt{4}>\sqrt{3}=> 2-\sqrt{3}>0$
b. $\sqrt{(3-\sqrt{11})^{2}}=\left | 3-\sqrt{11} \right |=\sqrt{11}-3$
Vì $3=\sqrt{9},\sqrt{9}<\sqrt{11}=> 3-\sqrt{11}<0$
c. $2\sqrt{a^{2}}=2\left | a \right |=2a (a\geq 0)$
d. $3\sqrt{(a-2)^{2}} =3\left | a-2 \right |=3(2-a)=6-3a ( a<2)$
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