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Which technique of integration would I use.

  1. May 3, 2010 #1
    1. The problem statement, all variables and given/known data
    ∫(9x^2)/(1+x^6 ) dx I was thinking of using U substitution but I can't figure it out.


    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. May 3, 2010 #2

    Char. Limit

    User Avatar
    Gold Member

    You actually could use u-substitution here. You just need to figure out...

    what function would have as it's derivative something that will cancel out when I u-sub?

    Now, what seems most easily canceled out here is the x^2 dx... so maybe if we had something like

    [tex]du=x^2 dx[/tex]

    with an appropriate coefficient, it could make the integral a lot easier.
     
  4. May 3, 2010 #3

    Mark44

    Staff: Mentor

    What have you tried? There aren't a lot of possibilities.
     
  5. May 3, 2010 #4
    I tried to let u=x^6 which made du 6x^5. This didn't get me anywhere. I also tried letting u= 9x^2 and that also got me nowhere.
     
  6. May 3, 2010 #5

    Char. Limit

    User Avatar
    Gold Member

    That's because it won't work if you do that. Try letting du = 9x^2 dx instead. That will get you farther. You just need to solve for u instead of solving for du.
     
  7. May 3, 2010 #6

    Mark44

    Staff: Mentor

    Try u = x^3
     
  8. May 3, 2010 #7
    Oh alright I've got it now!! Thanks so much.
     
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