Thread: Sum of an infinite series - comparing with a known series

Hi,

I'm doing a little revision and following through a sample exam paper.

Earlier in the current question, I found the Maclaurin Series for e^x and showed that it converges.

The last part of this question asks me to find:

sum 3^(n-1) / n!, n = 0 to infinity
Answer according to WolframAlpha

In short, I can't understand how this answer is derived. I can see x = 3 for e^x series would give me something close, but not the right answer.

It'd be great if you could offer a shove in the right direction .

Thanks in advance,
James

..

Thanks !