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Homework Help: Integration by parts

  1. Sep 27, 2007 #1
    How would you go about doing this:

    [tex]\int64x^2cos(4x)dx[/tex]

    The question specifically asks to integrate it by parts, so I integrated it that way a couple of times and came out with some long mess of sines and cosines, but it's not the right answer.

    Thanks.
     
  2. jcsd
  3. Sep 27, 2007 #2
    The approach is correct. The first thing I'd do is a substitution 4x->u just so that the numbers disappear. Then just integrate by parts twice. I suggest you try and post your attempt, so that we can see if it's just a simple algebraic mistake. Like I said, it's going in the right direction.
     
  4. Sep 28, 2007 #3
    Oops, I almost forgot about this. I actually was able to figure it out. Thanks though. :)
     
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