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Homework Help: Head scratching integral calculus hw

  1. Feb 28, 2005 #1
    hey guys, i need help on my integral calculus hw

    2) int(x*3*e^(x^7)) dx
    this one is just giving me insane problems
     
    Last edited: Feb 28, 2005
  2. jcsd
  3. Feb 28, 2005 #2

    cepheid

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    1) Try the substitution:

    u = (4-t)1/2

    du = -dt / 2(4-t)1/2

    Key thing here: you've got some expression of t and square root of some other expression involving t. Make a substitution to so that u is proportional to square root of t, and therefore t is in terms of u^2, and your integral now has u and u^2 in it. Much easier to work with. No square roots. Just polynomials. That's why I chose that substitution.
     
  4. Mar 1, 2005 #3
    Is this [tex]\int3 x e^x^7{dx}[/tex] or [tex]\int x^3 e^x^7{dx}[/tex]?

    As you have it written, it's a very strange order for multiplication. Either way, it doesn't seem to be a simple, straight-forward answer. The only way I seem to have found so far requires a reduction formula.
     
  5. Mar 1, 2005 #4

    dextercioby

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    For the integral
    [tex] \int x \ e^{x^{7}} dx [/tex]

    view the first attachement.

    For the integral
    [tex] \int x^{3} \ e^{x^{7}} dx [/tex]

    view the second...

    Daniel.
     

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  6. Mar 1, 2005 #5
    If he's still doing normal substitutions, it is doubtful that he is expected to know gamma integral transformations. I think there's a typo in the original poster's post.
     
  7. Mar 1, 2005 #6

    dextercioby

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    Then let him correct it,else his entire visit to PF has been useless...

    Daniel.
     
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