а) \(\dfrac{75b^5c^3}{50b^4c^4}\); б) \(\dfrac{2b}{b^2-9b}\); в) \(\dfrac{7x-7y}{x^2-y^2}\).

Сократим дроби, разложив знаменатели и числители на множители.

1. \(\dfrac{75b^5c^3}{50b^4c^4}=\dfrac{3b}{2c}\), при \(b\ne0\), \(c\ne0\).
2. \(\dfrac{2b}{b^2-9b}=\dfrac{2b}{b(b-9)}=\dfrac{2}{b-9}\), при \(b\ne0\), \(b\ne9\).
3. \(\dfrac{7x-7y}{x^2-y^2}=\dfrac{7(x-y)}{(x-y)(x+y)}=\dfrac{7}{x+y}\), при \(x\ne y\) и \(x\ne -y\).