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Math Help - [SOLVED] Derivative

  1. #1
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    [SOLVED] Derivative

     y=2cos(\frac {x}{2}) ,  \frac {d^2y}{dx^2}

    any hints were to begin
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  2. #2
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    First find the first derivative via chain rule:
    \begin{array}{rcl}\displaystyle  \frac{dy}{dx} & = & \displaystyle -2\sin \left(\frac{x}{2}\right) \cdot \left(\frac{x}{2}\right)' \\ & = & \displaystyle -2\sin \left(\frac{x}{2}\right) \cdot \frac{1}{2} \\ & = & \displaystyle -\sin \left(\frac{x}{2}\right) \end{array}

    Now apply the chain rule again to find the second derivative.
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  3. #3
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    Got it now the fraction was messing me

    thank you

    -1/2cos(x/2)
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