第12页 - 通城学典课时作业本八年级数学人教版南通专版

B

D

B

$2\sqrt{2}$

$2\sqrt{7}$

$2\sqrt{3}$

$解:(1)原式=2\sqrt{6}-5\sqrt{6}$

$=-3\sqrt{6}$

$解:(2)原式=\frac{3\sqrt{6}}{2}+\frac{\sqrt{6}}{2}$

$=2\sqrt{6}$

$解:(3)原式=4\sqrt {3}+4×\frac 1{2\sqrt {3}}-12\sqrt {3}-\frac {2}{\sqrt {3}}$

$=4\sqrt {3}+\frac {2\sqrt {3}}3-12\sqrt {3}-\frac {2\sqrt {3}}3$

$=-8\sqrt {3}$

$解:(4)原式=3\sqrt{5}+2×\frac {\sqrt{2}}{8}-2\sqrt{5}-\frac 14×5\sqrt{2}$

$=3\sqrt{5}+\frac {\sqrt{2}}4-2\sqrt{5}-\frac {5\sqrt{2}}4$

$=\sqrt{5}-\sqrt{2}$

B