第140页 - 经纶学典学霸八年级数学上下册【江苏国标】

C

B

C

$\frac{1}{3}$

3

1

5

$\frac{5\sqrt {6} -5}{2}$

$ \begin{aligned}解:原式&= \sqrt{48}-3×\frac{2\sqrt {3} }{3} \\ &=4\sqrt {3} -2\sqrt {3} \\ &=2\sqrt {3} . \\ \end{aligned}$

$ \begin{aligned}解:原式&=3+4-4\sqrt {3} +2\sqrt {3} +2\sqrt {3} \\ &=7. \\ \end{aligned}$

$ \begin{aligned}解:原式&=(42\sqrt {6} -16\sqrt {6} -6\sqrt {6} )×\frac{1}{2\sqrt {6} } ×\frac{1}{\sqrt{6}} \\ &=20\sqrt {6} ×\frac{1}{12} \\ &=\frac{5\sqrt {6} }{3}. \\ \end{aligned}$

$ \begin{aligned}解:原式&=6-3\sqrt {2} +2\sqrt {2} -2+1+2\sqrt {2} +2 \\ &=7 +\sqrt{2}. \\ \end{aligned}$

D

C