The MacLaurin Series for for .
So .
And finally .
Edit: Oops, didn't read the question fully stating not to use Taylor series hahaha. Ah well, it stays because it's beautiful
Hints
(i)
(ii) The following sequence is convergent
(iii) Express
(iv) Apply (i) to prove that
which is exactly the sum of the series.
Fernando Revilla
It is correct.
Hint : Express
Fernando Revilla