Tính: a) 6/7 * (-1/8) + 6/7 * (-3/4); b) (-7/17) * 7/12

* Hướng dẫn giải

a) $\frac{6}{7}.\left(\frac{-1}{8}\right)+\frac{6}{7}.(-\frac{3}{4})=\frac{6}{7}.[\left(\frac{-1}{8}\right)+\left(\frac{-3}{4}\right)]$

$=\frac{6}{7}.[\left(\frac{-1}{8}\right)+\left(\frac{-6}{8}\right)]=\frac{6}{7}.\frac{-7}{8}=\frac{-3}{4}$