Maxwell equations are 8. we need them to determine electric and magnetic field. the component of magnetic and electric field are 6. in linear algebra say for solving a system of equation with n free variable, we need n equations to solving it uniquely. here arises a question and that, why do we need 8 Maxwell equations to determine 6 field component? with a little attention to wave equation, we can understand they are 6 equations to determine component of field! with deep thinking to Maxwell equation, can be realized curl and divergence of field appear because of Helmholtz theorem, so the about question in general is true for Helmholtz theorem.