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Homework Help: Determination of a Potential

  1. Nov 5, 2007 #1
    1. The problem statement, all variables and given/known data

    I need to determine the potential of the following function:

    [tex]F = [2x(y^3 - z^3), 3x^2y^2, -3x^2z^2][/tex]

    The equation is given to be independent of path, and [tex]F \cdot dr = 0[/tex]

    3. The attempt at a solution

    [tex]\frac{\partial f}{\partial x} = 2xy^3 - 2xz^3 \Rightarrow f(x,y,z) = x^2y^3 - x^2z^3 + g(y,z)[/tex]

    [tex]\frac{\partial f}{\partial y} = 3x^2y^2 = 3x^2y^2 + \frac{\partial g}{\partial y} \Rightarrow g(y,z) = h(z)[/tex]

    [tex]\frac{\partial f}{\partial z} = -3x^2z^2 = \frac{\partial h}{\partial z} \Rightarrow h(z) = -x^2z^3[/tex]

    So, [tex]f(x,y,z) = x^2y^3 - 2x^2z^3[/tex]

    This answer doesn't check out. Taking the partial of f with respect to x, y, and z does not yield the initial equation. What am I missing? Is there a better way to go about this?

    The correct answer turns out to be [tex]x^2y^3 - x^2z^3[/tex], which is my initial equation for f without h(z).

    Last edited: Nov 5, 2007
  2. jcsd
  3. Nov 5, 2007 #2

    I think you got this line wrong
  4. Nov 5, 2007 #3
    ^ OK...what am I missing?

    Working backwards...

    [tex]\frac{\partial}{\partial z}(-x^2z^3) = -3x^2z^2[/tex]
  5. Nov 5, 2007 #4
    [tex]\frac{\partial f}{\partial z} = -3x^2z^2 = -3x^2z^2 + \frac{\partial h}{\partial z} \Rightarrow h(z) = 0 [/tex]

    Im having trouble with latex, but your partial f over partial z which is -3x^2z^2 = -3x^2z^2 + partial h over partial z. so, h(z) = 0=g(y,x)
    Last edited: Nov 6, 2007
  6. Nov 6, 2007 #5
    ^ Ahh...got it. I really shouldn't be doing this so late at night. :) Thanks!
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