第145页 - 亮点给力提优课时作业本八年级数学江苏版

A

$-2\sqrt {3}$

6

$= \sqrt {18}- \sqrt {18}$

$=0$

$= \sqrt {27}×\frac {2}{\sqrt 3}×2 \sqrt {2}-6 \sqrt {2}$

$=2 \sqrt {9}× 2\sqrt {2}-6\sqrt {2}$

$=12\sqrt {2}-6\sqrt {2}$

$=6\sqrt {2}$

解：原式$=2(a²-3)-a²+6a+6=2a²-6-a²+6a+6=a²+6a$

又$a=\sqrt {2}-1$

∴原式$=(\sqrt {2}-1)²+6(\sqrt {2}-1)=3-2\sqrt {2}+6\sqrt {2}-6=4\sqrt {2}-3$

C

B

2

$±\sqrt {7}$