A. 0
B. 2
C. 2x
D. 2(x+y+z)
If z(x,y) is the implicit function defined by x3+y3+z3=3xyz then xzx+yzy=
If u=3(lx+my+nz)2-(x2+y2+z2) and l2+m2+n2=1 then uxx+uyy+uzz=
If Z=1n(1+xr+yr) then Zxy=
If u=(x-y) (y-z) (z-x) then ux+uy+uz=