第158页 - 经纶学典新课时作业八年级数学上下册【江苏国标】

D

x＞4

B

A

二

-1或-7

$解:(1-\frac{1}{x+1})·\frac{x²-1}{x}$

$=\frac{x+1-1}{x+1}·\frac{x²-1}{x}$

$=\frac{x(x-1)(x+1)}{x(x+1)}$

$=x-1.$

$当x=\sqrt{2}+1时，x-1=\sqrt{2}+1-1=\sqrt{2}\ $

$ \begin{aligned} 解:原式&=-\sqrt{12}+2-\sqrt{3}-2 \\ &=-2\sqrt{3}+2-\sqrt{3}-2 \\ &=-3\sqrt{3} \\ \end{aligned}$

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

$ \begin{aligned} 解:原式&=\sqrt{4}+\sqrt{5}-2-(\sqrt{4}-\sqrt{3}) \\ &=2+\sqrt{5}-2-2+\sqrt{3} \\ &=\sqrt{5}+\sqrt{3}-2 \\ \end{aligned}$

$ \begin{aligned} 解:原式&=6-3\sqrt{5}+9-7 \\ &=8-3\sqrt{5} \\ \end{aligned}$