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Homework Help: Partial differentiation

  1. Aug 23, 2006 #1
    given f=ln(x^3+y^3+z^3-3xyz)To prove df/dx+df/dy+df/dz=3/(x+y+z)
    also finding (d^2/dx^2+...similar two more terms)f=? d => del
    & (d^2/dx^2+...........)^2f=?
    I have done the first part of the problem.The trick is to write e^f=x^3+y^3+z^3-3xyz and then to differentiate.
    However the next parts are coming hopelessly huge, by the same token.

    Please help.

    Kolahal Bhattacharya
  2. jcsd
  3. Aug 23, 2006 #2


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    Science Advisor

    One thing that will speed it up a little is the symmetry between x, y, and z. Given the derivative for one, you can easily write down the derivative for the others just by swapping variables.
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