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Help with integration

  1. Apr 29, 2009 #1
    1. The problem statement, all variables and given/known data
    Can someone please help me with integration of x(e^(-x-theta)) Thank you. My working is shown below

    3. The attempt at a solution
    u = x, du = 1 dx, dv = e^(-x-theta)) v = e^-x+theta+1 / theta + 1

    the rest can be seen in the attachment. Can you please check it out, it would be greatly appreciated.Thanks
     

    Attached Files:

  2. jcsd
  3. Apr 29, 2009 #2
    The attachment is pending approval so I can't see it.

    Use the substitution [tex] u = -x - \theta \Rightarrow x = -(u+\theta) \Rightarrow dx = -du [/tex]. So our integral is now [tex] \int (u + theta)e^u du [/tex].

    Now use integration by parts.
     
  4. Apr 29, 2009 #3
    ohhh wow thanks a lot!!
     
  5. Apr 29, 2009 #4

    HallsofIvy

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    The first thing I would do is write [itex]e^{-x- \theta}= e^{-x}e^{-\theta}[/itex] and factor out the [itex]e^{-\theta}[/itex]. Your integral is just [itex]e^{-\theta}\int xe^{-x}dx[/itex] which can be done by integration by parts.
     
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