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Homework Help: Derivative of f(z)=1/(z^2+1)?

  1. Oct 10, 2012 #1
    I don't know why I'm stuck on this problem or why I keep getting it wrong. The answer in my book is -2z/(z^2+1)^2, but I ended up with -(z^2+1)(2z)/(z^2+1)^2

    I don't understand where the whole z^2+1 in the numerator goes to. Isn't that how it's supposed to be chained? g(x) multiplied by g'(x)?

    Here's the work:

    0(z^2+1) - (1)(z^2+1)(2z)/(z^2+1)^2


    Could someone explain what I'm doing wrong?
    Last edited: Oct 10, 2012
  2. jcsd
  3. Oct 10, 2012 #2
    Absolutely nothing other than simplifying. Think cancel.
  4. Oct 10, 2012 #3


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    Science Advisor
    Homework Helper

    Where did the z^2+1 come from in your second term in the numerator? You just want g'(x). That doesn't need a chain rule.
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