- $\displaystyle \lim_{n \rightarrow \infty} \frac{x^n}{n!} = 0$ for all real $x$.
- $\displaystyle e^x = \sum_{n=0}^{\infty} \frac{x^n}{n!}$ for all real $x$.
- $\displaystyle e = \sum_{n=0}^{\infty} \frac{1}{n!}$
- The Binomial Series:
If $k$ is any real number and $|x|< 1$, then
$\displaystyle (1+x)^k = \sum_{n=0}^{\infty}{k \choose n}\, x^n = 1 + kx + \frac{k(k-1)}{2!}x^2 + \frac{k(k-1)(k-2)}{3!}x^3 + \ldots$
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