{% \nabla =\frac{\partial }{\partial x}\hat{\imath} + \frac{\partial }{\partial y}\hat{\jmath} +\frac{\partial }{\partial k}\hat{z}%}

{% \nabla \cdot \vec{v} = \frac{\partial v_x}{\partial x} + \frac{\partial v_y}{\partial y} + \frac{\partial v_z}{\partial z} %}