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Integration by parts

  1. Jan 20, 2008 #1
    1. The problem statement, all variables and given/known data

    [tex]\int[/tex](x-3x^2)cos(2x)dx

    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jan 20, 2008 #2
    What did you try?
     
  4. Jan 20, 2008 #3
    I think you should get [tex]\frac{3}{4}sin(2x)+C[/tex], but I could be wrong...show your work.
     
  5. Jan 20, 2008 #4
    I haven't done it, but that's wrong. The answer will need to have more than 2 terms.
     
    Last edited: Jan 21, 2008
  6. Jan 21, 2008 #5

    dynamicsolo

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    Homework Helper

    Quite so! A rule of thumb (probably isn't hard to prove) for integration of an nth-degree polynomial times sin kx, cos kx, or e^kx is that you will have (n+1) terms, running from x^n times the sinusoidal or exponential function down to a constant times that function. (OK, I'm not counting the arbitrary constant...)
     
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