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Homework Help: Need help differentiating a function

  1. Apr 30, 2012 #1
    1. The problem statement, all variables and given/known data

    f(x) = 2x * (10-x^2)^(1/2)

    Determine f'(x).

    2. The attempt at a solution

    f'(x) = 2x*(1/2) * (10-x^2)^(-1/2) * (-2x)
    = x * (-2x) * (10-x^2)^(-1/2)
    = -2x^2 * (10-x^2)^(-1/2)

    What am I doing wrong?
  2. jcsd
  3. Apr 30, 2012 #2


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    Science Advisor

    You aren't using the product rule. You have multiplied x by the derivative of [itex](10- x^2)^{1/2}[/itex], effectively treating that first "x" as though it were a constant. It is not.
  4. Apr 30, 2012 #3
    Doh! I'm such an idiot! Thanks for the quick response!
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