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Homework Help: Differentiation - Quotient rule

  1. Jan 5, 2010 #1
    1. The problem statement, all variables and given/known data

    Given y = x^2 + 6 / x find x if dy/dx equals 0 zero

    2. Relevant equations

    dy/dx = v du/dx - u dv/dx / v^2

    3. The attempt at a solution

    I have got as far as dy/dx = x^2 - 6 / x^2

    However then zero must equal Sqrt 6, which 2.44.... - can someone please confirm.

    Many thanks.
     
  2. jcsd
  3. Jan 5, 2010 #2

    rock.freak667

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    I didn't check to see if your derivative is correct, but I will assume it is. But solving x2-6=0 yields two answers √6 and -√6 . You have two answers for x.
     
  4. Jan 5, 2010 #3
    Hi Rock freak

    dy/dx = x^2 - 6 all over x^2

    So not sure how you arrived at x^2 - 6 = Sqrt +/- 6

    Can you check my derivative calc.

    Cheers
     
  5. Jan 5, 2010 #4

    rock.freak667

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    Well your derivative looks correct.


    [tex]\frac{x^2-6}{x^2}=0 \Rightarrow x^2-6=0[/tex]

    x2-a2=(x-a)(x+a). See how x= ±√6 ?
     
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