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Homework Help: Integrating by parts

  1. Nov 9, 2011 #1
    1. The problem statement, all variables and given/known data

    ∫r^3/(4+r^2)^(1/2) dr

    2. Relevant equations


    3. The attempt at a solution

    I know that integration by parts must be used. I tried doing it with 4+r^2 as u, but kept running into issues..then I got an answer but it appears to be wrong. I guess I am not sure how to do this.
  2. jcsd
  3. Nov 9, 2011 #2


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    Homework Helper

    First substitute r^2=t, then integrate by parts.

  4. Nov 9, 2011 #3


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    Science Advisor
    Homework Helper

    I don't think it needs integration by parts. I'd do a simple u substitution. u=r^2+4, like AnnieF suggested. What 'issues' were you running into?
  5. Nov 10, 2011 #4
    The substitution [itex]u=r^2[/itex] would be significantly easier to deal with. One can then use parts or another substitution to make the integral elementary.
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