Решение:
а) $\frac{-1}{2} + \frac{-1}{2} = \frac{-(1 + 1)}{2} = \frac{-2}{2} = -1;$
б) $\frac{-1}{3} + \frac{-1}{3} = \frac{-(1 + 1)}{3} = \frac{-2}{3} = -\frac{2}{3};$
в) $\frac{-2}{3} + \frac{-1}{3} = \frac{-(2 + 1)}{3} = \frac{-3}{3} = -1;$
г) $\frac{-2}{7} + \frac{-5}{7} = \frac{-(2 + 5)}{7} = \frac{-7}{7} = -1;$
д) $\frac{-7}{12} + \frac{-1}{12} = \frac{-(7 + 1)}{12} = \frac{-8}{12} = -\frac{2}{3}.$
Ответ:
а) −1;
б) $-\frac{2}{3};$
в) −1;
г) −1;
д) $-\frac{2}{3}.$