12. Вычислите разность: а) $$\frac{7}{8} - \frac{3}{4}$$; б) $$\frac{9}{10} - \frac{2}{5}$$; в) $$\frac{3}{4} - \frac{4}{15}$$; г) $$\frac{7}{6} - \frac{6}{7}$$

Решение:

1. \[ \frac{7}{8} - \frac{3}{4} = \frac{7}{8} - \frac{6}{8} = \frac{1}{8} \]
2. \[ \frac{9}{10} - \frac{2}{5} = \frac{9}{10} - \frac{4}{10} = \frac{5}{10} = \frac{1}{2} \]
3. \[ \frac{3}{4} - \frac{4}{15} = \frac{45}{60} - \frac{16}{60} = \frac{29}{60} \]
4. \[ \frac{7}{6} - \frac{6}{7} = \frac{49}{42} - \frac{36}{42} = \frac{13}{42} \]