2) Сократите дробь: а) \(\frac{a^2b^5}{ab^7}\); б) \(\frac{-63xy^5}{81xy^4}\).

1. \(\frac{a^2b^5}{ab^7}=a^{2-1}b^{5-7}=\frac{a}{b^2}\).
2. \(\frac{-63xy^5}{81xy^4}= -\frac{63}{81}y^{5-4}=-\frac{7y}{9}\).

Ответ: а) \(\frac{a}{b^2}\); б) \(-\frac{7y}{9}\).