# cauchy's integral formula for derivatives question

I've been working through Marsden's Complex Analysis book, and I've come to a question where I'm not quite sure if I've got it. I would love some help.

question: Let f be analytic on a region, A, and let g be a closed curve in A. For any $z_0$ in A not on g, show that:

$\int_{g}\frac{f^{'}(a)}{{a - z_0}}da$ = $\int_{g}\frac{f(a)}{{(a - z_0)}^2}da$

and the followup question: how can you generalize this result?