第35页 - 江苏版启东中学作业本七年级数学（上下册）

C

±7

4

$-\frac {30}{17}$

$-\frac {138}{49}$

-2或0或2

解：原式$=(-\frac {5}{7})×(-\frac {4}{3})×(-\frac {7}{15})$

$=-\frac {4}{9}$

解：原式$=72×\frac {9}{4}×\frac {4}{9}×\frac {5}{18}$

$=20$

解：原式$=-\frac {11}{5}×\frac {25}{11}×(-\frac {2}{5})$

$=2$

解：原式$=(-\frac {3}{4})×(-\frac {7}{3})×(-\frac {6}{7})$

$=-\frac {3}{2}$

解：原式$=(-\frac {3}{4}-\frac {1}{6}+\frac {5}{12})×(-36)$

$=-\frac {3}{4}×(-36)- \frac {1}{6}×(-36)+\frac {5}{12}×(-36)$

$=27+6-15$

$=18$

解：原式$ = (-\frac {1}{42})÷ [\frac {1}{6}+\frac {2}{3}-(\frac {3}{14}+\frac {2}{7})$

$ = (-\frac {1}{42})÷(\frac {5}{6}-\frac {1}{2})$

$=(-\frac {1}{42})×3$

$=-\frac {1}{14}$

解：∵$\frac {-\frac {15}{17}}{-\frac {13}{15}}=\frac {15×15}{17×13}=\frac {225}{221}$，$\frac {225}{221}＞1$

∴$-\frac {15}{17}＜-\frac {13}{15}$