第31页 - 江苏版实验班提优训练数学七年级上下册答案

A

C

确定积的符号，并把绝对值相乘

乘法的交换律

乘法的结合律

解：原式$=-9+30-28+2$

$=-5$

解：原式$=(-100+\frac {1}{16})×8$

$=-800+\frac {1}{2}$

$=-799\frac {1}{2} $

C

A

-130

解：原式$=\frac {3}{2}×\frac {5}{4}×\frac {7}{6}×···×\frac {21}{20}×\frac {2}{3}×\frac {4}{5}×\frac {6}{7}×\frac {8}{9}× ···×\frac {20}{21}$

$=\frac {3}{2}×\frac {2}{3}×\frac {5}{4}×\frac {4}{5}×\frac {7}{6}×\frac {6}{7}×···×\frac {21}{20}×\frac {20}{21}$

$=1×1×1×···×1$

$=1$