第138页 - 经纶学典学霸八年级数学上下册【江苏国标】

C

B

$\sqrt {5}\ $

$2\sqrt {7}\ $

$3\sqrt {2}\ $

2

$ \begin{aligned}解:原式&=4\sqrt {3} -6×\frac {\sqrt {3} }{3}+3\sqrt {3} \\ &=5\sqrt {3} . \\ \end{aligned}$

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

$ \begin{aligned} 解:原式&=\frac{2}{3}·3\sqrt {x} +6·\frac {\sqrt {x} }{2}-x·\frac{\sqrt{x}}{x} \\ &=2\sqrt {x} +3\sqrt {x} - \sqrt{x} \\ &=4\sqrt {x} . \\ \end{aligned}$

$ \begin{aligned}解:原式&=4b·\frac{\sqrt {ab} }{b}-\frac{2}{a}·a \sqrt{ab}-5\sqrt {ab} \\ &=4 \sqrt{ab}-2 \sqrt{ab}-5 \sqrt{ab} \\ &= -3 \sqrt{ab}. \\ \end{aligned}$

B

D