208 Найдите сумму: a) 4/7 + (-6/7); б) 1/3 + (-2/7).

a) \(\frac{4}{7} + (-\frac{6}{7}) = \frac{4}{7} - \frac{6}{7} = \frac{4 - 6}{7} = \frac{-2}{7} = -\frac{2}{7}\) б) \(\frac{1}{3} + (-\frac{2}{7}) = \frac{1}{3} - \frac{2}{7} = \frac{7}{21} - \frac{6}{21} = \frac{7 - 6}{21} = \frac{1}{21}\)