1. The problem statement, all variables and given/known data Find all second partial derivatives of z=arctan((x+y)/(1-xy)) 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.