\(\dfrac{-3}{4}.\dfrac{4}{7}+\dfrac{-3}{5}.\dfrac{-3}{7}+\dfrac{2}{-5}=\dfrac{-3}{7}+\dfrac{-3}{5}.\dfrac{-3}{7}+\dfrac{2}{-5}=\dfrac{-3}{7}\left(1+\dfrac{-3}{5}\right)+\dfrac{2}{-5}=\dfrac{-3}{7}.\dfrac{2}{5}+\dfrac{2}{-5}=\dfrac{2}{5}\left(\dfrac{-3}{7}-1\right)=\dfrac{2}{5}.\dfrac{-10}{7}=\dfrac{-4}{7}\)
\(-\dfrac{3}{4}\cdot\dfrac{4}{7}+\left(-\dfrac{3}{5}\right)\cdot\left(-\dfrac{3}{7}\right)+\left(-\dfrac{2}{5}\right)\)
\(=-3\cdot\dfrac{1}{7}+\dfrac{9}{35}+\left(-\dfrac{2}{5}\right)\)
\(=-\dfrac{3}{7}+\dfrac{9}{35}+\left(-\dfrac{2}{5}\right)\)
\(=-\dfrac{4}{7}\)
\(\dfrac{-3}{4}.\dfrac{4}{7}+\dfrac{-3}{5}.\dfrac{-3}{7}+\dfrac{2}{5}\)
\(=\dfrac{-3}{7}+\dfrac{-3}{5}.\dfrac{-3}{7}+\dfrac{2}{5}\)
\(=\dfrac{-3}{7}.\left(1+\dfrac{-3}{5}\right)+\dfrac{2}{5}\)
\(=\dfrac{-3}{7}.\dfrac{2}{5}+\dfrac{2}{5}=\dfrac{2}{5}.\left(-\dfrac{3}{7}+1\right)\)
\(=\dfrac{2}{5}.\dfrac{4}{7}=\dfrac{8}{35}\)
Chúc bạn học tốt!!!
