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Derivative question

  1. Oct 9, 2007 #1
    I forgot how to take these derivatives. Could someone tell me the rule/work it out.

    P = (doS1 + d1So) / (d1 + S1)

    dP/dS1 = ?

    I think it should be (denominator*d(numerator) - d(denom.)num.) / denom^2

    but that gets the wrong answer.
     
  2. jcsd
  3. Oct 9, 2007 #2

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Are do and d1 constants? In other words, is this the same as
    [tex]P(x,y)= \frac{ax+ by}{b+ x}[/tex]?
    with z= do, b= d1, x= S1, y= So

    In that case, yes, the partial derivative of P with respect to x is "(denominator*d(numerator) - d(denom.)num.) / denom^2"
    (If So is also a constant, not a variable, then it is not a partial derivative but the same rule applies.)
     
  4. Oct 9, 2007 #3
    OK, but the d(denominator) with respect to S1 which is a variable is 1, right?
     
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