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Math Help - Related rates problem

  1. #1
    Junior Member
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    Related rates problem

    Let be the area of a circle with radius . If , find when .
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    Moderator edit: Deleted post restored. Thread closed.
    Last edited by mr fantastic; November 19th 2010 at 09:01 PM. Reason: Restored deleted question.
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  2. #2
    MHF Contributor Unknown008's Avatar
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    \dfrac{dA}{dt} = \dfrac{dA}{dr} \times \dfrac{dr}{dt}

    You know dr/dt.

    You know that A = \pi r^2

    Find dA/dr and plug in r = 1 and plug that in the chain rule equation.
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  3. #3
    MHF Contributor harish21's Avatar
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    A=\pi\;r^2

    \dfrac{dA}{dt} = 2\pi r \; \dfrac{dr}{dt}
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