Giải thích các bước giải:
$\dfrac{-1}{2} + \dfrac{3}{21} + \dfrac{-2}{6} + \dfrac{-5}{30}$
$= \dfrac{-1}{2} + \dfrac{3}{21} - \dfrac{2}{6} - \dfrac{5}{30}$
$= \dfrac{-1}{2} + \dfrac{1}{7} - \dfrac{1}{3} - \dfrac{1}{6}$
$= \dfrac{-21}{42} + \dfrac{6}{42} - \dfrac{14}{42} - \dfrac{7}{42}$
$= \dfrac{-21 + 6 - 14 - 7}{42}$
$= \dfrac{-36}{42}$
$= \dfrac{-6}{7}$
$C$húc bạn học tốt !
