и) 7/18 - (-8/9) = к) 2/28 - 7/42-

Ответ: 23/18; -1/12

1. \( \frac{7}{18} - \left(-\frac{8}{9}\right) = \frac{7}{18} + \frac{8}{9} = \frac{7}{18} + \frac{8 \cdot 2}{9 \cdot 2} = \frac{7}{18} + \frac{16}{18} = \frac{7 + 16}{18} = \frac{23}{18} \)
2. \( \frac{23}{28} - \frac{7}{42} = \frac{23 \cdot 3}{28 \cdot 3} - \frac{7 \cdot 2}{42 \cdot 2} = \frac{69}{84} - \frac{14}{84} = \frac{69 - 14}{84} = \frac{55}{84} = \frac{5 \cdot 11}{7 \cdot 12} = \frac{5}{12} \)

Ответ: 23/18; -1/12