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Math Help - Partial derivatives..

  1. #1
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    Post Partial derivatives..

    I'm looking for the indicated second-order partial derivative for the function f(x,y).

    f(x,y)=(1+2xy^2)^8

    What I have is:

    fx=(2y^2)^8 fy=(4xy)^8

    fxx=0 fyy=(4x)^8

    fxy=(4y)^8 fyx=4^8

    I'm not good at the language of math so I'm not sure if I need to go on and if so, if I have even done what I have right. Any help is more than appreciated.
    Last edited by halborse; November 20th 2008 at 07:46 PM. Reason: Made error when writing function
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  2. #2
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    Quote Originally Posted by halborse View Post
    I'm looking for the indicated second-order partial derivative for the function f(x,y).

    f(x,y)=(1+4xy^2)^8

    What I have is:

    fx=(2y^2)^8 fy=(4xy)^8

    fxx=0 fyy=(4x)^8

    fxy=(4y)^8 fyx=4^8

    I'm not good at the language of math so I'm not sure if I need to go on and if so, if I have even done what I have right. Any help is more than appreciated.
    When you take partial derivative w.r.t x, consider y as a constant.
    So f_x=8(1+4xy^2)^74y^2
    f_y=(8(1+4xy^2)^78xy
    Can you continue from here?
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  3. #3
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    Thanks

    I made an error when I wrote it down. I have since corrected this, but thank you for your help thus far. I just needed to check my numbers against someone else and I think you helped enough for me to do so. thank you once again.
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  4. #4
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    my math is weak

    I still can't see how to make this work. and when I use my Ti-89 I just end up with y=0. Wish it would show me the steps. Maybe you can. Please?
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