@JohnRennie Sir I’m learning Green’s Theorem. My book writes $$ \mathbf A = U \nabla V - V \nabla U $$ and , consequently, for $A_n$ $$ A_n = U \frac{\partial V}{\partial n} - V \frac{\partial U}{\partial n}$$
@JohnRennie Yes. Let’s take for simplicity $$\mathbf A = U ~grad V $$ $$\mathbf A \cdot n = U \frac {\partial V}{\partial x} n_x + \frac{\partial V}{\partial y} n_y + \frac{\partial V}{\partial z}n_z$$
