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Homework Help: Partial derivatives and power rule

  1. Feb 28, 2012 #1
    1. The problem statement, all variables and given/known data

    ∂f/∂x (xy -1)2 = 2y(xy-1)

    3. The attempt at a solution

    I would think the answer would be


    I don't understand where the y comes from in 2y
  2. jcsd
  3. Feb 28, 2012 #2


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    Science Advisor
    Homework Helper

    It comes from the chain rule. Look it up!
  4. Feb 28, 2012 #3
    It looks like they're using u substitution

    (u)2 = 2u

    u = xy - 1
    du or ∂f/∂x(not sure about the notation) = y

    2u * y = 2y(u), insert u = 2y(xy-1)
  5. Feb 28, 2012 #4
    i solved the problem before I saw dick's reply
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