4. Сократите дробь: а) \(\frac{5a^3}{15a^2b}\); в) \(\frac{42m^3n^4}{28m^4n^3}\).

1. \(\frac{5a^3}{15a^2b}=\frac{5a^2\cdot a}{5a^2\cdot3b}=\frac{a}{3b}\).
2. \(\frac{42m^3n^4}{28m^4n^3}=\frac{42}{28}\cdot\frac{n^4}{m n^3}=\frac{3n}{2m}\).

Ответ: а) \(\frac{a}{3b}\); в) \(\frac{3n}{2m}\).