б) \(\frac{3}{4} - \frac{1}{2}\) д) \(\frac{5}{9} - \frac{5}{12}\) з) \(\frac{19}{21} - \frac{11}{15}\)

Решение:

б) \( \frac{3}{4} - \frac{1}{2} = \frac{3}{4} - \frac{2}{4} = \frac{1}{4} \)

д) \( \frac{5}{9} - \frac{5}{12} = \frac{20}{36} - \frac{15}{36} = \frac{5}{36} \)

з) \( \frac{19}{21} - \frac{11}{15} = \frac{95}{105} - \frac{77}{105} = \frac{18}{105} = \frac{6}{35} \)

Ответ: б) \(\frac{1}{4}\), д) \(\frac{5}{36}\), з) \(\frac{6}{35}\).