4.208 Найдите сумму: a) \(\frac{4}{7} + (-\frac{6}{7})=\) b) \(\frac{4}{9} + \frac{2}{3}=\) д) \(\frac{5}{12} + \frac{7}{9}=\) б) \(\frac{1}{3} + (-\frac{2}{7})=\) г) \(-\frac{4}{7} + \frac{2}{3}=\) e) \(\frac{8}{15} + (-\frac{7}{10})=\)

**Решение:** a) \(\frac{4}{7} + (-\frac{6}{7}) = \frac{4}{7} - \frac{6}{7} = \frac{4-6}{7} = \frac{-2}{7} = -\frac{2}{7}\) b) \(\frac{4}{9} + \frac{2}{3} = \frac{4}{9} + \frac{2 \times 3}{3 \times 3} = \frac{4}{9} + \frac{6}{9} = \frac{4+6}{9} = \frac{10}{9} = 1\frac{1}{9}\) д) \(\frac{5}{12} + \frac{7}{9} = \frac{5 \times 3}{12 \times 3} + \frac{7 \times 4}{9 \times 4} = \frac{15}{36} + \frac{28}{36} = \frac{15+28}{36} = \frac{43}{36} = 1 \frac{7}{36}\) б) \(\frac{1}{3} + (-\frac{2}{7}) = \frac{1}{3} - \frac{2}{7} = \frac{1 \times 7}{3 \times 7} - \frac{2 \times 3}{7 \times 3} = \frac{7}{21} - \frac{6}{21} = \frac{7-6}{21} = \frac{1}{21}\) г) \(-\frac{4}{7} + \frac{2}{3} = -\frac{4 \times 3}{7 \times 3} + \frac{2 \times 7}{3 \times 7} = -\frac{12}{21} + \frac{14}{21} = \frac{-12+14}{21} = \frac{2}{21}\) e) \(\frac{8}{15} + (-\frac{7}{10}) = \frac{8}{15} - \frac{7}{10} = \frac{8 \times 2}{15 \times 2} - \frac{7 \times 3}{10 \times 3} = \frac{16}{30} - \frac{21}{30} = \frac{16-21}{30} = \frac{-5}{30} = -\frac{1}{6}\) **Ответы:** a) \(-\frac{2}{7}\) b) \(1\frac{1}{9}\) д) \(1 \frac{7}{36}\) б) \(\frac{1}{21}\) г) \(\frac{2}{21}\) e) \(-\frac{1}{6}\)