Đáp án:
Giải thích các bước giải:
a) $\dfrac{-2}{5}$ + $\dfrac{3}{-4}$ + $\dfrac{6}{7}$ + $\dfrac{3}{4}$ + $\dfrac{2}{5}$
= $\dfrac{-2}{5}$ + $\dfrac{-3}{4}$ + $\dfrac{6}{7}$ + $\dfrac{3}{4}$ + $\dfrac{2}{5}$
= ($\dfrac{-2}{5}$ + $\dfrac{2}{5}$) + ($\dfrac{-3}{4}$ + $\dfrac{3}{4}$) + $\dfrac{6}{7}$
= 0 + 0 + $\dfrac{6}{7}$
= $\dfrac{6}{7}$
b) $\dfrac{-1}{8}$ + $\dfrac{7}{9}$ + $\dfrac{-7}{8}$ + $\dfrac{6}{7}$ + $\dfrac{2}{14}$
= ($\dfrac{-1}{8}$ + $\dfrac{-7}{8}$) + ($\dfrac{6}{7}$ + $\dfrac{2}{14}$) + $\dfrac{7}{9}$
= -1 + ($\dfrac{12}{14}$ + $\dfrac{2}{14}$) + $\dfrac{7}{9}$
= -1 + 1 + $\dfrac{7}{9}$
= 0 + $\dfrac{7}{9}$
= $\dfrac{7}{9}$
c) $\dfrac{5}{11}$ + $\dfrac{16}{22}$ + $\dfrac{-12}{4}$ + $\dfrac{-2}{11}$
= ($\dfrac{5}{11}$ + $\dfrac{16}{22}$ + $\dfrac{-2}{11}$) + $\dfrac{-12}{4}$
= ($\dfrac{10}{22}$ + $\dfrac{16}{22}$ + $\dfrac{-4}{22}$) + $\dfrac{-12}{4}$
= 1 + $\dfrac{-12}{4}$
= $\dfrac{-12}{4}$
d) $\dfrac{7}{23}$ + $\dfrac{-10}{18}$ + $\dfrac{-4}{9}$ + $\dfrac{16}{23}$
= ($\dfrac{7}{23}$ + $\dfrac{16}{23}$) + ($\dfrac{-10}{18}$ + $\dfrac{-4}{9}$)
= 1 + $\dfrac{-10}{18}$ + $\dfrac{-8}{18}$
= 1 + (-1)
= 0
