1. ## proof of summation

How can I prove the following equality? :

$\sum_{n=0}^{\infty} \frac{(\lambda\cdot e^{t})^{n}}{n!}=e^{\lambda\cdot e^{t}}$

2. ## Re: proof of summation

That's a defining quality of e^x...
List of representations of e - Wikipedia, the free encyclopedia
And replace the "x" in the article with \lambda e^t