I am trying to solve the following problem. I have gotten a fair way into it, but the last steps elude me. Here is the problem:
So, we already know that , because
Letting and :
Getting back to the matter at hand, we can take out the :
We can also write it as:
This gives the same series, because
is the same as
I don't know what to do to get the though.
Any help would be appreciated.