A. 0
B. -z
C. Z
D. 3z
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=