b) 5/7 . -2/11 + 5/7 . -9/11 + 5/7

* Hướng dẫn giải

b) $\frac{5}{7}.\frac{-2}{11}+\frac{5}{7}.\frac{-9}{11}+\frac{5}{7}$

$$\begin{gathered} =\frac{5}{7}.\left(\frac{-2}{11}+\frac{-9}{11}+1\right) \\ =\frac{5}{7}.\left(\frac{-11}{11}+1\right) \\ =\frac{5}{7}.\left(-1+1\right) \\ =\frac{5}{7}.0 \\ =0 \end{gathered}$$