Which of the following vector fields is solenoidal (divergence-free)?
⟨x,y,z⟩\langle x, y, z \rangle⟨x,y,z⟩
⟨y,z,x⟩\langle y, z, x \rangle⟨y,z,x⟩
⟨ex,ey,ez⟩\langle e^x, e^y, e^z \rangle⟨ex,ey,ez⟩
⟨xz,yz,−z2⟩\langle xz, yz, -z^2 \rangle⟨xz,yz,−z2⟩