Quick math question!

  1. How do I evaluate (d^2)/(dxdy)?

    Is it just d/dx*d/dy?

    Thanks!
     
  2. jcsd
  3. tiny-tim

    tiny-tim 26,053
    Science Advisor
    Homework Helper

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

    (and it's also ∂/∂y*∂/∂x)
     
  4. 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. Integral

    Integral 7,345
    Staff Emeritus
    Science Advisor
    Gold Member

    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. tiny-tim

    tiny-tim 26,053
    Science Advisor
    Homework Helper

    ohhh! :smile:

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

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

    ∂(∂F/∂y)/∂x :wink:
     
  7. Oh! I got it now! Thanks fellas!
     
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