Monday, 3 February 2014

convergence divergence - Prove that $x^n/n!$ converges to $0$ for all $x$

Prove that $a_n=x^n/n! \to 0$ for all $x$



Here is what I tried, but it seems to lead to nowhere.




Choose $\epsilon > 0$. We need to show that there exists $N\in \mathbb{N}$ such that for all $n>N$ we have $|a_n| < \epsilon$



So, $|(x^n/n!)| < \epsilon \implies |x^n| < n!\cdot \epsilon$ (since $n!$ is positive we ignore the absolute signs). So $|x|/(\epsilon^{1/n}) < [n!^{(1/n)}]$.
Now I am stuck in solving this for $n$, and hence finding $N$ ...

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