Ответ:

  1. \(\frac{6}{7}-\frac{2}{3}=\frac{18}{21}-\frac{14}{21}=\frac{4}{21}\).
  2. \(\frac{5}{12}-\frac{5}{6}=\frac{5}{12}-\frac{10}{12}=-\frac{5}{12}\).
  3. \(\frac{7}{12}-\frac{3}{8}=\frac{14}{24}-\frac{9}{24}=\frac{5}{24}\).
  4. \(\frac{9}{14}-\frac{19}{35}=\frac{45}{70}-\frac{38}{70}=\frac{7}{70}=\frac{1}{10}\).

Ответ: а) \(\frac{4}{21}\); б) \(-\frac{5}{12}\); в) \(\frac{5}{24}\); г) \(\frac{1}{10}\).