Is that the sum of ( -1 )^n / ( n! ) or ( ( -1 )^n / n )! and maybe the tranformation is trivial, but why does this equal e^(-1)?
Edit: I guess the factorial of a fraction doesn't make much sense.
Edit: I guess the factorial of a fraction doesn't make much sense.
As far as the second question goes, that's taken to be the definition e^x := \sum_{n=0}^{\infty} (x^n)/(n!)