y=f(x) to z=f(x,y) ???? Help My question is : when z=f(x,y) is written down ... it's assume that we're working in the cartesian plane with z on the vertical axis, x and y on the horizontal right? And they're not going to mix that around on me unless otherwise stated? So I can associate the variables x and y and z in my head --as meaning the x y and z coordinate respectively ...and theyren not going to have x be the 'y' coordinate on the graph and x be the 'z' coordinate....??? z=f(x,y) is the y=f(x) of 2 variables?