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U-substitution problem

  1. Oct 17, 2011 #1
    1. The problem statement, all variables and given/known data
    1~~0 (x^7)/sqrt(4-3x^16) dx




    3. The attempt at a solution

    There really isn't one. I am as clueless as one can get in calculus. I know that I am supposed to substitute the variable "u" in for a section of this problem, but really don't know anything after that. I understand derivatives but that is about it. If someone could walk me through this problem it'd be great.
     
  2. jcsd
  3. Oct 17, 2011 #2

    LCKurtz

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    You know that when you make a u substitution, you need the du to be in the integral. You have x7 sitting there. What u might give you an x7 in the du? Think about that.
     
  4. Oct 17, 2011 #3
    7x^6???
     
  5. Oct 17, 2011 #4

    LCKurtz

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    No, you are just guessing. If you want to get x7 in the answer for du, what must u be? You got x6 in your answer, not x7. C'mon, you can do better than that.
     
    Last edited: Oct 17, 2011
  6. Oct 18, 2011 #5
    I told you I don't know much about calculus...so just saying "come on" isn't going to magically help me get the answer.

    Is u x^7? Or 4-3x^16?
     
  7. Oct 18, 2011 #6

    HallsofIvy

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    If you honestly have no idea what to do, even with LCKurtz's very good hint, there isn't a lot we can do for you. You really need to talk to your teacher about this kind of problem.
     
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