3) а) \(\frac{3(a-b)}{a(b-a)}\); б) \(\frac{4x-8y}{3y-6x}\); в) \(\frac{p^2-5pq}{10q-2p}\); г) \(\frac{c^3-7c^2d}{7d^3-cd^2}\).

1. Так как \(b-a=-(a-b)\), то \(\frac{3(a-b)}{a(b-a)}=-\frac{3}{a}\).

2. \(\frac{4x-8y}{3y-6x}=\frac{4(x-2y)}{-3(x-2y)}=-\frac{4}{3}\).

3. \(\frac{p^2-5pq}{10q-2p}=\frac{p(p-5q)}{-2(p-5q)}=-\frac{p}{2}\).

4. \(\frac{c^3-7c^2d}{7d^3-cd^2}=\frac{c^2(c-7d)}{d^2(7d-c)}=-\frac{c^2}{d^2}\).

Ответ: а) \(-\frac{3}{a}\); б) \(-\frac{4}{3}\); в) \(-\frac{p}{2}\); г) \(-\frac{c^2}{d^2}\).