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Math Help - Partial differentiation with a log function

  1. #1
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    Question Partial differentiation with a log function

    How do I do this particular question?
    f (x,y) = ln (x + y)
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  2. #2
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    What do you actually want to compute? Is it \frac{\partial f}{\partial x} or \frac{\partial f}{\partial y}?
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by Krizalid View Post
    What do you actually want to compute? Is it \frac{\partial f}{\partial x} or \frac{\partial f}{\partial y}?
    you can pick one and do it. if that's the question, great, if not, the poster can practice by doing the other one similarly.
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    I need to do both for this question, not just one. If someone could help me with it, I would greatly appreciate it.
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by njr008 View Post
    I need to do both for this question, not just one. If someone could help me with it, I would greatly appreciate it.
    for \frac {\partial f}{\partial x} you treat x as a variable and y as a constant. so y is just like any other number now. it might as well be 2 or something.

    Thus, by the chain rule:

    \frac {\partial f}{\partial x} = \frac 1{x + y} \cdot 1 = \frac 1{x + y}

    do a similar thing for \frac {\partial f}{\partial y}
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