The problem:

arctan(x/3)

I assume you derive it: 1/(1+(x/3)²)

then put it in the proper formation: 1/(1- (-x/3)²)

so then I get the sigma of -1^2n -x/3²^n

and then I have to take the integral?

I just don't get what to do, like the proper formation. Why do I have to keep the -1 and -x/3 seperate if they are both to the 2n power?

And in an unrelated note, when do you have to change the index? I don't get that AT ALL.

FML. thanks