## Calculus (3rd Edition)

$$\frac{d}{dx}\left( \frac{ax+b}{cx+d}\right) =\frac{da-bc}{(cx+d)^2}.$$
By the quotient rule, we have $$\frac{d}{dx}\left( \frac{ax+b}{cx+d}\right)=\frac{(cx+d)(a)-(ax+b)(c)}{(cx+d)^2}\\ =\frac{da-bc}{(cx+d)^2}.$$