Câu 6 C
Do $\sqrt[]{A^2}=|A|$
Câu 7 B
Do $\sqrt[]{A^2}=|A|$
Câu 8 C
Do $\sqrt[]{x^2}=5⇒|x|=5⇒x=±5$
Câu 9 C
Do $\sqrt[]{16x^2y^4}=\sqrt[]{(4.x.y^2)^2}=4|x|y^2$
Câu 10 C
$\dfrac{\sqrt[]7+\sqrt[]5}{\sqrt[]7-\sqrt[]5}+\dfrac{\sqrt[]7-\sqrt[]5}{\sqrt[]7+\sqrt[]5}$
$=\dfrac{(\sqrt[]7+\sqrt[]5)^2}{7-5}+\dfrac{(\sqrt[]7-\sqrt[]5)^2}{7-5}$
$=\dfrac{7+5+2\sqrt[]{7.5}+7+5-2\sqrt[]{7.5}}{2}$
$=\dfrac{24}{2}=12$
Câu 11
$=\dfrac{2.(3-2.\sqrt[]2)}{9-(2.\sqrt[]2)^2}+\dfrac{2.(3+2.\sqrt[]2)}{9-(2.\sqrt[]2)^2}$
$=\dfrac{6-4.\sqrt[]2+6+4.\sqrt[]2}{1}=12⇒CHỌN$ $C$
