All derivatives are partial derivatives
fx = df/du *du/dx + df/dv*dv/dx
fy = df/du *du/dy + df/dv*dv/dy
I used to know this stuff backwards but I am having trouble relearning it because my class notes never seem to match my problem sheets.
If somebody could just work through this one question for me, I'm sure it would all come back:
Use the Chain Rule (only) to find the first order derivatives fx and fy:
f(x,y) = v/u, where u = x+y, v = x-y