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Math Help - Derivative problem?

  1. #1
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    Derivative problem?

    Could someone help me with this problem. I am coming up with 1/((sqrt(4x^2-1))+1) and it is wrong. Thanks

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  2. #2
    Moo
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    Hello,
    Quote Originally Posted by johnny4lsu View Post
    Could someone help me with this problem. I am coming up with 1/((sqrt(4x^2-1))+1) and it is wrong. Thanks

    You didn't use the chain rule !

    [f(g(x))]'=g'(x) f'(g(x))

    Here, it gives :
    [\tan^{-1}(u(x))]'=u'(x) \cdot \frac{1}{(u(x))^2+1}

    Do you understand ?
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  3. #3
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    let me try again moo! thanks
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  4. #4
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    i'm still can't figure it out Moo!! Could you walk me through it!
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  5. #5
    Moo
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    Quote Originally Posted by johnny4lsu View Post
    i'm still can't figure it out Moo!! Could you walk me through it!
    Okay !

    First, you should calculate the derivative of u(x), namely \sqrt{4x^2-1}
    You'll have to use the chain rule once again !

    That is (\sqrt{v(x)})'=\frac{v'(x)}{2 \sqrt{v(x)}}

    u'(x)=\left(\sqrt{4x^2-1}\right)'=\frac{8x}{2 \sqrt{4x^2-1}}=\frac{4x}{\sqrt{4x^2-1}}

    Does it help ?

    If not, I'd suggest you have a look here : Chain rule - Wikipedia, the free encyclopedia

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  6. #6
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    Thanks a lot moo!!! I figured it out!!
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