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Homework Help: Limits question

  1. Nov 6, 2007 #1
    1. The problem statement, all variables and given/known data
    x->1 [tex]\frac{tan^{-1} (x - pi/4)}{x -1}[/tex]

    2. Relevant equations
    None that I know of

    3. The attempt at a solution
    Indeterminate form, so use L'Hopital's rule

    Differentiate the top, then differentiate the bottom.
    The differential of the denominator is just 1.
    However I have no idea how to differentiate the numerator.

    Thanks for any help
  2. jcsd
  3. Nov 6, 2007 #2
    derivative of arctan(u) is: 1/(1+u^2)
    Last edited: Nov 6, 2007
  4. Nov 6, 2007 #3
    [tex]\frac{d}{dx}tan^{-1} (x) = \frac {1}{x^2+1}[/tex]
  5. Nov 6, 2007 #4
    Thanks guys.
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