5.478

а) \(\frac{3}{7} + \frac{1}{14} = \frac{6}{14} + \frac{1}{14} = \frac{7}{14} = \frac{1}{2}\), \(\frac{3}{7} - \frac{1}{14} = \frac{6}{14} - \frac{1}{14} = \frac{5}{14}\), \(\frac{1}{2} + \frac{5}{14} = \frac{7}{14} + \frac{5}{14} = \frac{12}{14} = \frac{6}{7}\). Ответ: \(\frac{6}{7}\) б) \(\frac{1}{9} + \frac{1}{12} = \frac{4}{36} + \frac{3}{36} = \frac{7}{36}\), \(\frac{1}{9} - \frac{1}{12} = \frac{4}{36} - \frac{3}{36} = \frac{1}{36}\), \(\frac{7}{36} + \frac{1}{36} = \frac{8}{36} = \frac{2}{9}\). Ответ: \(\frac{2}{9}\)