I am not sure what is intended by the suggestion "to expand the sum in ."
The series converges in the operator norm to whenever . Therefore as .
I have no idea how to solve this:
where symmetric , .
Derive x in the limit .
We are just interested in the sign of . It is helpful to expand the sum in . What happens as ? Which terms in the sum are non-zero? Which terms dominate as ?
Thanks for your answer!
Expanding in means solving this term with repect to the -th component of .
Your post looks plausible to me, but are we allowed to do this? I forgot to mention the following hint in the description:
Consider the limit . Setting will yield a different result!