Si $y = \frac{ax^2}{(x-a)(x-b)(x-c)} + \frac{bx}{(x-b)(x-c)} + \frac{c}{x-c} + 1$, demuestre que:
$$\frac{y'}{y} = \frac{1}{x} \left( \frac{a}{a-x} + \frac{b}{b-x} + \frac{c}{c-x} \right)$$