# Homework Help: Tough limtis, answers involve e

1. Feb 20, 2013

### e^(i Pi)+1=0

limit as n→∞ of $\frac{(2t)^n}{n!}$ and $\frac{(-t)^n}{n!}$

Answers are e2t-1 and e-t-1 but I don't know how to work them out, thanks.

edit: btw these are series

2. Feb 20, 2013

### Dick

If those are series you should fix up your question showing the limits of the series. Do you know $e^a=\Sigma^\infty_0 \frac{a^n}{n!}$?

3. Feb 20, 2013

### haruspex

Starting at n=1, it would seem? That would be unusual.

4. Feb 21, 2013

### HallsofIvy

These are easy if you know that
$$\sum_{n=0}^\infty \frac{x^n}{n!}= e^x$$