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Basic calculus problem

  1. May 4, 2013 #1
    1. The problem statement, all variables and given/known data

    See attached.

    2. Relevant equations


    3. The attempt at a solution

    I integrated the equation with respect to x to obtain
    ∫[itex]\frac{d}{dx}[/itex](x[itex]e^{-x}[/itex][itex]\frac{df}{dx}[/itex])dx+∫n[itex]e^{-x}[/itex]fdx= constant
    The first term on the left hand side goes to zero as x, df/dx are bounded at 0, infinity. This leaves the expression ∫n[itex]e^{-x}[/itex]fdx= constant which is not the one given.
     

    Attached Files:

    Last edited by a moderator: May 4, 2013
  2. jcsd
  3. May 4, 2013 #2

    tiny-tim

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    hi eas123! :smile:

    what happened to m ? :confused:
     
  4. May 4, 2013 #3
    Hi. :-)

    What do you mean? I don't know how to derive the expression.
     
  5. May 4, 2013 #4

    tiny-tim

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    your expected answer, ##\int_0^{\infty} e^{-x}f_n(x)f_m(x) dx = 0##, has an "m" in it

    i don't see an "m" in your actual work
     
  6. May 4, 2013 #5
    So where have I gone wrong?
     
  7. May 4, 2013 #6

    tiny-tim

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    i'm completely confused :redface:

    you seem to be solving a different problem :confused:

    start with ##e^{-x}f_n(x)f_m(x) dx = 0##, and integrate it :smile:
     
  8. May 4, 2013 #7

    SammyS

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    The following is an image of the attachment. Please notice that the result you are to prove contains both n and m . That's what tiny-tim is telling you.

    attachment.php?attachmentid=58464&d=1367661781.jpg
     
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