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Quick math question!

  1. Mar 1, 2012 #1
    How do I evaluate (d^2)/(dxdy)?

    Is it just d/dx*d/dy?

  2. jcsd
  3. Mar 1, 2012 #2


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    hi btbam91! :smile:
    quick answer: yup! :biggrin:

    (and it's also ∂/∂y*∂/∂x)
  4. Mar 1, 2012 #3
    Hmmm, double check my work because I must be doing something wrong!

    I'm looking to evaluate -(d^2)/(dxdy) of F, where F = ax^2+bxy+cy^2

    So for dF/dx, I get 2ax+by. For dF/dy, I get bx+2cy.

    So, multiplying both together and accounting for the negative sign:

    -[(2ax+by)*(bx+2cy)]= -[2abx^2+4acxy+b^2xy+2bcy^2]

    The answer is supposed to be -b according to the solution manual (that doesn't show the solution :p)

    Am I missing something here? Thanks!
  5. Mar 1, 2012 #4


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    Do not multiply, but apply each differential sequentially. So after finding the first differential, do the second on the resulting expression. Order is not critical.
  6. Mar 1, 2012 #5


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    ohhh! :smile:

    i assumed you meant ∂/∂x of ∂/∂y …

    you ∂/∂y it first, then you ∂/∂x it …

    ∂(∂F/∂y)/∂x :wink:
  7. Mar 1, 2012 #6
    Oh! I got it now! Thanks fellas!
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