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Homework Help: What is the derivative for arctan(2/x)?

  1. Jun 17, 2005 #1
    What is the derivative for


    I know it's generally: [(1/a)arctan(x/a)]' = 1/(x^2 + a^2); but in my case its x^-1!

    Thanks for any help.
  2. jcsd
  3. Jun 17, 2005 #2


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    The formula to remember is

    [tex]Arctg'(x) = \frac{1}{1+x^2}[/tex]

    So using the chain rule,

    [tex]Arctg'(f(x)) = \frac{f'(x)}{1+[f(x)]^2}[/tex]

    which gives the derivative of Arctg for any argument.
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