# Math Help - integral of exp(-x) * x^n

1. ## integral of exp(-x) * x^n

integration from 0 to infinity, of exp(-x) * x^n with respect to x.

2. ## Re: integral of exp(-x) * x^n

Define $f(n)\equiv\int_0^{\infty}x^ne^{-x}\,dx$ and use integration by parts to show that:

$f(n)=nf(n-1)$ and hence:

$f(n)=n!$

3. ## Re: integral of exp(-x) * x^n

by the way how do you post in integral typeset like that?

4. ## Re: integral of exp(-x) * x^n

It is done using $\LaTeX$. There is a forum here dedicated to its usage, and there are many good tutorials online too.