1. ## help with integral

Hello users of this forum. I used to love calculus when I was in university but now my memory play me tricks when trying to remember properties and ways to calculate integrals.

I would like to have a brief explanation about how to solve and valuate this integral I'm attaching. My doubts are both with the way the integral should be solved and also how to valuate the result in the (0, +infinite) domain.

Thanks to all the participants in the forum for being here for us!

Rodrigo

2. ## Re: help with integral

If you've to calculate:
$\int_{0}^{\infty} x\cdot\alpha\cdot e^{-\alpha x}dx$
Try integration by parts.

3. ## Re: help with integral

Do you want to solve $\displaystyle \int x\times ae^{-ax}~dx$ ?

If so, $\displaystyle \int uv' = uv - \int u'v$

In your case make $u = x , v' = ae^{-ax}$ should be straight foward from there...