Its not that we don't want to solve it...its just that we can't think of a clever way to do it! We're discussing that same limit here.
--Chris
The rules do not prevent you from using a series expansion of:
Or avoiding series the fact that and the definition of (3rd) derivative to give:
(here denotes a function such that the limit as goes to of this function divided by goes to zero) which will allow the evaluation of the limit.
I suspect though that you might consider all this to be cheating as this is tantamount to either L'Hopital's rule and/or the use of series)
RonL