1. The problem statement, all variables and given/known data z = cos(x^2 + 3y^2) x = ucosv y=usinv find dz/dv 2. Relevant equations 3. The attempt at a solution I think I can do these fairly well, but I'm a little unsure of the "protocol" for which variables to put back in. Sometimes (in this case) I can't really put everything as v. So I choose to put everything as u and v since they are on the same "level." for example, I get that (dv/dv) = (dy/dv)(dz/dy) + (dx/dv)(dz/dx) When taking those partials and multiplying out ( leaving variables as they are.. ) = - ucos(v)sin(x^2 + 3y^2)6y + usin(v)sin(x^2 + 3y^2)2x So what is the technique? Replace all x and y with ucosv and usinv respectively, and leave u in the partial derivative?