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Solving derivative with roots in denominator

  1. Feb 4, 2009 #1
    1. The problem statement, all variables and given/known data

    i have to get f'(x) using the limit definition of the derivative (lim as h approches 0 f(x)= (f(x+h) - f(x)) /h) and I don't know where to start. f(x)= 3/(sqrt(1+x^2)

    2. Relevant equations
    what do I do with the (sqrt(1+x^2)

    3. The attempt at a solution
    I have gotten to lim as h approches 0 f(x)= (f(x+h) - f(x)) /h) = 3-3/ sqrt(1+(x+h)^2- sqrt(1-x^2)/h
    Last edited: Feb 4, 2009
  2. jcsd
  3. Feb 4, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper

    Uh, it's lim h->0 of (f(x+h)-f(x))/h. Your difference quotient is kind of messed up. Can you fix it up first?
  4. Feb 5, 2009 #3


    Staff: Mentor

    I might add that the numerator won't be 3 - 3 as you show.

    3/a - 3/b != (3 - 3)/(stuff in the denominator)

    Before you start adding the terms in the numerators of fractions, the denominators have to be the same.
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