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Homework Help: Integration by parts

  1. Sep 22, 2008 #1
    1. The problem statement, all variables and given/known data
    Integrate [tex]\int{\frac{lnx}{x^4}dx}[/tex]

    2. Relevant equations

    3. The attempt at a solution

    I get this:
    [tex]u = ln x, du = \frac{1}{x}[/tex]
    [tex]dv=x^4, v=\frac{x^5}{5}dx[/tex]
    [tex]\frac{(lnx)x^5}{5}-\int{\frac{x^5}{5}*\frac{1}{x}dx} = \frac{(lnx)x^5}{5}-\frac{6x^6}{5}dx}[/tex]

    Am I doing this right?
  2. jcsd
  3. Sep 22, 2008 #2
    Your dv should be the integral of 1/x^4, not x^4.
  4. Sep 22, 2008 #3
    Hmm, ok. So what would be v?
  5. Sep 22, 2008 #4
    The integral of x^(-4), which is 1/-3 * x^-3
  6. Sep 22, 2008 #5
    Oooh, ok. Thanks for your help!
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