1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Staff Emeritus
    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!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook