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Integrating exponentials

  • Thread starter Brewer
  • Start date
212
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1. Homework Statement
I'm being dead thick, but I can't remember how to integrate an exponential function.
[tex]\int x^3e^{-\alpha x^2}dx[/tex]


2. Homework Equations



3. The Attempt at a Solution
I reckon that this shouldn't be too complex, but I've totally forgotten how to go about this question. The [tex]x^3[/tex] term means that it can't be integrated like I would normally do (i.e. [tex]\int ke^x = ke^{\frac{x}{k}}[/tex]) can it? I've also tried substituting [tex]u=x^2[/tex] into it and following that through, but it doesn't seem to get anywhere.

Is this really simple, and my recent lack of practice with the techniques is just failing me, or there something more complicated about it?

Please assist, this is doing my head in!
 
Last edited:

Answers and Replies

AlephZero
Science Advisor
Homework Helper
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Substituting u = x^2 is a good first move.

You will get a simpler integral involving e^{-au} which you can solve by integration by parts.
 
HallsofIvy
Science Advisor
Homework Helper
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[tex]\int x^3e^{-\alpha x^2}dx= \int x^2 e^{-\alpha x^2} (xdx)[/tex]

Now, as others have said, let u= x2.
 
212
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Oh so I was going right.

I hate integration by parts.
 

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