1. The problem statement, all variables and given/known data Given that the surface x^7y^2+y^4z^6+z^8x^8+9xyz=12 has the equation z=f(xy) in a neighbourhod of the point (1,1,1) with f(x,y) differentiable, find the derivatives. df/dx (1,1) = ??? d^2f/dx^2 (1,1) = ??? 2. Relevant equations 3. The attempt at a solution df/dx (1,1) I got -24/23 or 7x^6y^2+6y^4z^5(dz/dx)+8z^7x^8(dz/dx)+8z^8x^7+9yz+9xy(dz/dx) d^2f/dx^2: I tried doing the same thing and squaring the derivative when they came up again but it didn't work.