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Homework Help: Integration by parts?

  1. Jan 15, 2006 #1
    integration by parts??

    just trying to figure out this integral int(x^2 (1+x^3)^4 dx)

    when i integrate by substitution i get anti deriv.... 1/15 (1+x^3)^5

    which is not the same (but close when u plug in values of x) to

    1/15*x^15 +1/3*x^12 + 2/3*x^9 + 2/3*x^6 + 1/3*x^3

    am i going about this wrong?....i'm letting u = 1 + x^3...what
     
  2. jcsd
  3. Jan 15, 2006 #2

    Tom Mattson

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    Your answer is right. You must have made a mistake when plugging in values of x.
     
  4. Jan 15, 2006 #3
    bleh, mistake.
     
  5. Jan 15, 2006 #4
    1/15*x^15 +1/3*x^12 + 2/3*x^9 + 2/3*x^6 + 1/3*x^3 is the value i got from maple



    1/15 (1+x^3)^5 is the value i got by hand....


    plug in values of x....u get different results...

    if x=1...

    the first one u get 31/15...the second is 32/15
     
  6. Jan 15, 2006 #5

    HallsofIvy

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    (1/15)(1+ x^3)^5= (1/15)x^15+ (1/3)x^12+ (2/3)x^9+ (2/3)x^6+ (1/3)x^3+ 1/15.

    Do the words "constant of integration" mean anything to you?
     
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