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Homework Help: How to integrate this problem

  1. Apr 27, 2010 #1
    1. The problem statement, all variables and given/known data
    S(x(x+1)1/2) dx


    2. Relevant equations



    3. The attempt at a solution
    u=x+1
    du=1
    x=u-1

    S(x(u)1/2) du

    S(((u-1)(u)1/2) du

    S((u2-u)1/2) du

    S(u-u1/2) du

    S((1/2)u2-(2/3)u3/2)

    =(1/2)(x+1)2-(2/3)(x+1)3/2) + C


    Online homework says it's wrong... Where did I mess up?
     
  2. jcsd
  3. Apr 27, 2010 #2

    tiny-tim

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    Hi tjohn101! :smile:

    (have an integral: ∫ :wink:)
    Neither of these lines is correct. :redface:

    (u-1)√u = u√u - √u :wink:
     
  4. Apr 27, 2010 #3
    Ahhhh thank you. I didn't notice I had done that :/
     
  5. Apr 27, 2010 #4
    Hmmm I ended up getting

    (2/5)(x+1)5/2-(2/3)(x+1)3/2 + C

    Sound right?
     
  6. Apr 28, 2010 #5

    tiny-tim

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    Hi tjohn101! :smile:

    (just got up :zzz: …)

    Yes :smile:but perhaps you should put it in the same form as the question, ie √(x+1) times an ordinary polynomial in x ? :wink:
     
  7. Apr 28, 2010 #6
    Thank you for your help!
     
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