5.409 Найдите сумму или разность:

Решение:

1. \( \frac{1}{5} + \frac{1}{7} = \frac{7}{35} + \frac{5}{35} = \frac{12}{35} \)
2. \( \frac{4}{7} + \frac{1}{9} = \frac{36}{63} + \frac{7}{63} = \frac{43}{63} \)
3. \( \frac{9}{11} + 0 = \frac{9}{11} \)
4. \( \frac{1}{2} + \frac{1}{6} = \frac{3}{6} + \frac{1}{6} = \frac{4}{6} = \frac{2}{3} \)
5. \( \frac{1}{2} + \frac{7}{9} = \frac{9}{18} + \frac{14}{18} = \frac{23}{18} = 1\frac{5}{18} \)
6. \( \frac{1}{3} - \frac{1}{4} = \frac{4}{12} - \frac{3}{12} = \frac{1}{12} \)
7. \( \frac{4}{9} - \frac{2}{5} = \frac{20}{45} - \frac{18}{45} = \frac{2}{45} \)

Ответ: a) \( \frac{12}{35} \), б) \( \frac{43}{63} \), г) \( \frac{9}{11} \), д) \( \frac{2}{3} \), е) \( 1\frac{5}{18} \), ж) \( \frac{1}{12} \), и) \( \frac{2}{45} \).