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Homework Help: Implicit Differentiation

  1. Mar 8, 2009 #1
    Use Implicit Differentiation to find y" if

    xy + y - x = 1

    so far i got

    1y + dy/dx - dx/dx = 1/dx

    then i did

    y + y' - 1 = 0
    y' = 1-y

    i dont understand how to get the y" . i dont think i even have y' done right!
  2. jcsd
  3. Mar 8, 2009 #2


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    Homework Helper
    Gold Member

    Careful; [tex]\frac{d}{dx}(xy)\neq y[/tex]....you need to use the product rule.

    And, [tex]\frac{d}{dx}(1)=0\neq\frac{1}{dx}[/tex]
  4. Mar 8, 2009 #3


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    Gold Member

    Perhaps to provide additional help, once you correctly find the first derivative, express it in terms of y' alone and then differentiate implicitly again.
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