Đề bài

Tính: a)     \(\frac{-2}{9} + \frac{7}{-9}\) b)    \(\frac{1}{-6} + \frac{13}{-15}\) c)     \(\frac{5}{-6} + \frac{-5}{12}+\frac{7}{18}\)

Lời giải chi tiết

a)\(\frac{-2}{9} + \frac{7}{-9}\\= \frac{-2}{9} + \frac{-7}{9}\)\(=\frac{(-2) +(-7)}{9}\\= \frac{-9}{9}\\=-1\)b)\(\frac{1}{-6} + (\frac{13}{-15})\) \(=\frac{-1}{6}+ \frac{-13}{15}\\= \frac{-5}{30}+\frac{-26}{30}\\=\frac{(-5) +(-26)}{30}\\=\frac{-31}{30}\)c)\(\frac{5}{-6} + \frac{-5}{12}+\frac{7}{18}\\= \frac{-5}{6}+ \frac{-5}{12}+\frac{7}{18}\)\(=\frac{(-30)}{36}+\frac{-15}{36}+\frac{14}{36}\)\(=\frac{(-30)+(-15)+14}{36}\\=\frac{-31}{36}\)