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Concept question-exponential function derivatives (calc II)

  1. Sep 10, 2007 #1
    Concept question--exponential function derivatives (calc II)

    Ok, so there is an example on my textbook that asks for the derivative of y = x^2.

    --after applying ln on both sides, if finally gets to the lny = xlnx step.

    But after this step, it just states y'/y = x(1/x)+ lnx(1). I understand it is just the prod. rule on the right, but can anyone explain why it went from lny to y'/y ? Is this a property or formula that they used?

    Thank you.
     
  2. jcsd
  3. Sep 10, 2007 #2
    they used implicit differentiation on the lhs.

    You might remember using it on things like xy=1 or equations like that in Calc I.

    so (ln y)' = 1/y * dy/dx which gives the y'/y
     
  4. Sep 10, 2007 #3

    Hurkyl

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    Chain rule?
     
  5. Sep 10, 2007 #4
    Oh, I see. Thank you.
     
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