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Math Help - Help please

  1. #1
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    Help please

    Help please-assignment-4-question-3.pngAny help with this would be wonderful
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  2. #2
    MHF Contributor ebaines's Avatar
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    Re: Help please

    From the equation  \frac 1 {R} = \frac 1 {R_1} + \frac 1 {R_2} you can rearrange to make 'R' the subject:

     R = \frac {R_1R_2}{R_1 + R_2}

    Now it's simply a matter of taking the derivative of this with respect to time, and substituting the values for  R_1, \ R_2, \ R'_1 and  R'_2 that you've been given.
    Last edited by ebaines; May 1st 2013 at 07:02 AM.
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  3. #3
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    Re: Help please

    Or use "implicit differentiation" as it stands. Do you know that dx^{-1}/dt= -x^{-2}dx/dt?
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