Show that the vector field
\displaystyle\mathbf{v}=x\sin y\mathbf{i}+y\sin x\mathbf{j}-z(\sin x+\sin y)\mathbf{k}
is solenoidal.
We have
v_{x}=x\sin y\, so that {\frac{\partial v_{x}}{\partial x}}=\sin y\,
Also,
v_{\mathrm{y}}=y\sin x so that {\frac{\partial v_{\mathrm{y}}}{\partial y}}=\sin x\,
Finally,
v_{z}=-z(\sin x+\sin y) so that {\frac{\partial v_{z}}{\partial z}}=-(\sin x+\sin y)
Therefore,
\nabla\cdot\mathbf{v}=\sin y+\sin x-(\sin x+\sin y)=0and hence v is solenoidal.