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## Homework Statement

In the open unit disk D = {(x,y)|x

^{2}+ y

^{2}< 1} give a forumla for:

(a) [tex]\frac{\partial \sum ^{inf}_{n=0} (xy) ^{n}}{\partial x}[/tex]

(b) [tex]\frac{\partial (e^{x+y} \int ^{y}_{x} e^{-t} dt)}{\partial y}[/tex]

## Homework Equations

## The Attempt at a Solution

Ok this is on my exam review sheet and he gave us the solutions to go along with it.. I don't know if I wasn't paying attention in class or what but I don't remember doing anything like this.

His first step for a is [tex]\sum ^{inf}_{n=0} (xy)^{n} = \frac{1}{1 - xy}[/tex] if xy < 1 (But for all (x,y)[tex]\in[/tex] D xy < 1

I'm already confused at this point. Can someone please let me know what is going on here? Thanks