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Thread: derivatie question

  1. #1
    Junior Member
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    Apr 2007
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    derivatie question

    Here is the problem f(x) = sqrt(4x + 9)
    then f' (x) = ?
    Here is what I did:
    1/2 d/dx[4x+9]^-1/2
    1/(2*sqrt(4x+9))
    This is where I get stuck.
    Please give me a push.
    Thank you!
    Keith
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by keith View Post
    Here is the problem f(x) = sqrt(4x + 9)
    then f' (x) = ?
    Here is what I did:
    1/2 d/dx[4x+9]^-1/2
    1/(2*sqrt(4x+9))
    This is where I get stuck.
    Please give me a push.
    Thank you!
    Keith

    $\displaystyle
    \frac{d}{dx}h(g(x)) = g'(x) h'(g(x))
    $

    In this case $\displaystyle g(x)=4x+9$ and $\displaystyle h(x)=\sqrt(x)$, so:

    $\displaystyle
    \frac{d}{dx}h(g(x)) =\frac{d}{dx}\sqrt(4x+9)= 4 (1/2) (4x+9)^{-1/2}=2 (4x+9)^{-1/2}
    $

    RonL
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