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Math Help - Classifying critical points

  1. #1
    Newbie
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    Oct 2009
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    Classifying critical points

    Hi all,

    So I'm trying to work out an exam question, regarding finding the critical point of a function, fractions always cause me a headache in calculus questions.

    so anyways, heres the function in question, I just need to find partial derivitives on it, and I'm struggling

    xy+(4/x)+(2/y)
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  2. #2
    Junior Member
    Joined
    Aug 2009
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    For something like that you could rewrite the equation as:

    xy+4x^{-1}+2y^{-1}

    Does that make it easier to find the partials?
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  3. #3
    Newbie
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    Oct 2009
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    Thanks!
    But differentiating that, gives me
    y-4x^-2
    and
    x-2y^-2.
    Usually i have to do a simultaneous equation from that point, but how do i when i have these ^-2's getting in my way? I just get tangled up here
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