Cách làm cho bạn:
a) \(\frac{-3}{7}+\frac{5}{13}+\frac{-4}{7}\)
\(=\left ( \frac{-3}{7}+\frac{-4}{7} \right )+\frac{5}{13}\)
\(=-1+\frac{5}{13}\)
\(=\frac{-13}{13}+\frac{5}{13}\)
\(=\frac{-8}{13}\)
b) \(\frac{-5}{21}+\frac{-2}{21}+\frac{8}{24}\)
\(=\frac{-7}{21}+\frac{8}{24}\)
\(=\frac{-1}{3}+\frac{1}{3}=0\)
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