Hey guys.

Look at this question please.

I have two paths, and I need to proof the thing in red.

They give a tip due, they say to show first that the equation in green is correct and then using Taylor development, to proof the red equation.

I'm still in the first phase, in the green equation. I know it got something to do with Cauchy's integral formula but I cant see how...

Any idea guys?

Thanks a lot.