# Help solving integrals when doing radial probability densities in the Bohr model

1. Oct 12, 2014

### Brianrofl

1. The problem statement, all variables and given/known data

Image: http://puu.sh/ca93V/7eb9abf342.png [Broken]

2. Relevant equations

Ok I know to use this guy http://puu.sh/ca95c/ad0155a4d6.png [Broken]

Which then turns into this http://puu.sh/ca96W/68802e045c.png [Broken] (except from .5a to 4a, not 0 to a)

3. The attempt at a solution

I get lost on trying to integrate this thing. All these problems involving radial probability densities seem to have weird integrals. I've tried letting x = r/a but that also just gets weird.

If I could get an explanation on this topic I'd really appreciate it.

Last edited by a moderator: May 7, 2017
2. Oct 13, 2014

### haruspex

Are you saying you just need help integrating $r^4e^{-kr}.dr$? Please post your attempt, as per forum rules.