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Homework Help: Derivatives of arctan((x+y)/(1-xy))

  1. Jul 30, 2011 #1
    1. The problem statement, all variables and given/known data

    Find all second partial derivatives of

    2. Relevant equations

    d/dx of arctan(x) is 1/(1+x^2)

    3. The attempt at a solution

    Not sure how to proceed... I don't want the answer, just an idea as to how to move forward.

    My attempt at finding the first derivative...

    z'=(1/(1+(x+y/(1-xy)) * (x(1-xy) - (x+y(-y)) / (1-xy)^2

    Is this correct? If it is, I honestly don't know how to find the second derivative...

    On another note, can someone tell me how I can use math notation instead of plain text, to make the equations and such easier to read? Thanks guys.
  2. jcsd
  3. Jul 30, 2011 #2


    User Avatar
    Homework Helper

    Take care of the parentheses. Check the derivative of the arctan function.

    To make your task easier, remember the addition formula :
    Can you write the function z(x,y) in a simpler form?
    As for Math notations, go to "advanced" and click on the 'Σ'.
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