Đặt thừa số chung (-3/4+2/5):3/7 + (3/5+-1/4)

* Hướng dẫn giải

$\begin{array}{l}\left(\frac{-3}{4}+\frac{2}{5}\right):\frac{3}{7}+\left(\frac{3}{5}+\frac{-1}{4}\right):\frac{3}{7}\\ =\left(\frac{-3}{4}+\frac{2}{5}\right).\frac{7}{3}+\left(\frac{3}{5}+\frac{-1}{4}\right).\frac{7}{3}\\ =\frac{7}{3}.\left(\frac{-3}{4}+\frac{2}{5}+\frac{3}{5}+\frac{-1}{4}\right)\\ =\frac{7}{3}.\left(\frac{-3}{4}+\frac{-1}{4}+\frac{2}{5}+\frac{3}{5}\right)\\ =\frac{7}{3}.\left(-1+1\right)\\ =0\end{array}$