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Calc II question help

  1. Oct 1, 2007 #1
    This deals with inverse functions:

    suppose g(x) is the inverse of f(X) and G(X) = 1/g(X). If f(3) = 3 and f'(3) = 1/9, find G'(3).

    Does anyone know how to answer this question?

    Thanks.

    I was thinking of using the formula g'(x) = 1/f'(g(X)), but the G(X) is throwing me off.
     
  2. jcsd
  3. Oct 1, 2007 #2

    ptr

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    [tex]f'(x)= \frac{1}{f^{-1}'(x)}[/tex]
     
  4. Oct 1, 2007 #3
    tthat is not what is being asked...
     
  5. Oct 1, 2007 #4

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    If G(x)= 1/ g(x)= g-1 then, by the chain rule, G'= -1g(x)-2 g'(x). Since g(x) is f-1(x), g'(x)= 1/f'(x).
     
  6. Oct 1, 2007 #5
    I still don't get it. Can anyone explain it using the actual numbers to derive an answer? I need to understand this before the exam.
     
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