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Math Help - Simple Derivative

  1. #1
    Newbie
    Joined
    Oct 2008
    Posts
    21

    Smile Simple Derivative

    I need som help with this.
    Im having trouble finding the derivative of (the first image 1.)

    The Answer should be (image 2)

    But all I get is (image 3)

    Were does the √(x-1) come from?

    THANKS
    Attached Thumbnails Attached Thumbnails Simple Derivative-derivativefinal.jpg  
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  2. #2
    MHF Contributor
    Joined
    Nov 2008
    From
    France
    Posts
    1,458
    Hi

    f(x) = (x-4) \: \sqrt{x-1}

    To find the derivative use the formula of the derivative of a product
    (uv)' = u'v + uv'

    Here
    u(x) = x-4 then u'(x) = 1
    v(x) = \sqrt{x-1} then v'(x) = \frac{1}{2\sqrt{x-1}}

    Therefore
    f'(x) = \sqrt{x-1} + \frac{x-4}{2\sqrt{x-1}}
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