What is the <x> for given wavefunction A*exp(-(\sqrt{}Cm/2h)x^{}2)?

[fredrick08]

Homework Statement

calculate <x>, when \Psi(x,t)=A*exp(-(\sqrt{}Cm/2h)x^{}2

Homework Equations

<x>=\int\Psi^{}*x\Psidx over all space..
\intexp(-\alphax^{}2)=\sqrt{}\pi/\alpha

The Attempt at a Solution

ok know how to do this but how do i do the intergral... my maths isn't so good, and the book does it very very vague... i know <x>=0 but don't know how to prove it.

 

[fredrick08]

so far I've got down to

A²\intexp(-(\sqrt{}Cm/2h)x²)x dx, fomr -a/2 to a/2

 

[millitiz]

Hi fredrick.
Just want to make sure, you aren't going to integrate the whole space, right?
Well, there are several ways of solving this problem.
So the easiest one is, well, do the math.
So it seems like you are stuck and don't know how to do the integration.

Just a very small hint, what is the anti derivative of exp(ax^2)*x?
not sure? Well, obviously, it is going to relate to exp(ax^2), right? There is no other way to get this term, right?
So it is probably something with exp(ax^2).
Know, try to differentiate your "guess" function. And remember the chain rule. And see if it is the same as exp(a*x^2)x
Once you get your guessed function right, I think you can find the anti derivative of your function.
And the rest is pretty much plug in

I'll tell the other way, which doesn't even involve doing all the dirty job after you finish your calculation :D
Good luck!

 

[Matterwave]

Actually, if you have an x as well as an exp(x^2) as the integrand, there is no need to even worry about integrating exp(x^2).

Make a substitution u=ax^2, du=2ax and simply do it that way.