第121页 - 江苏版实验班提优训练数学八年级上下册答案

C

-1-a

3

$\sqrt{7}+\sqrt {6}\ $

12

$2\sqrt{3}-2 $

$解:原式=\sqrt {8}-\sqrt{2}+ \sqrt{(-5)^{2} }$

$ \begin{aligned} &=2\sqrt{2}-\sqrt {2} +5 \\ &=\sqrt {2} +5. \\ \end{aligned}$

$ \begin{aligned}解:原式&=(\sqrt{3}-\sqrt {6} )²-(2+\sqrt{5})(2-\sqrt{5}) \\ &=3-6\sqrt{2}+6-(4-5) \\ &=3-6\sqrt{2}+6+1 \\ &=10-6\sqrt{2}. \\ \end{aligned}$

$ \begin{aligned}解:原式&= \sqrt{16}-\sqrt{6}+2\sqrt{6} \\ &=4+\sqrt{6}. \\ \end{aligned}$

$解:∵x=\sqrt {5} -1，\ $

$∴x²+5x-6$

$=(\sqrt{5}-1)²+5×(\sqrt{5}-1)-6$

$=5-2\sqrt{5}+1+5\sqrt{5}-5-6$

$=-5+3\sqrt{5}.$

$ \begin{aligned} 解:原式&=\frac {20}{3}\sqrt {30} ÷(-\frac {3}{2}\sqrt {1\frac {1}{2}} ) \\ &=-\frac {40}{9}\sqrt {60} \\ &=-\frac {80}{9}\sqrt {15} \\ \end{aligned}$

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