$$\eqalign{ & \mathop E\limits^ \to \left( {x,t} \right) = {E_0}\cos \left( {kx - \omega t} \right)\,\,{\widehat a_y} \cr & \mathop H\limits^ \to \left( {x,t} \right) = {H_0}\cos \left( {kx - \omega t} \right){\widehat a_z} \cr} $$

$$\eqalign{ & \mathop E\limits^ \to \left( {x,t} \right) = {E_0}\cos \left( {kx - \omega t} \right)\,\,{\widehat a_y} \cr & \mathop H\limits^ \to \left( {x,t} \right) = {H_0}\cos \left( {kx - \omega t - {\pi \over 2}} \right){\widehat a_z} \cr} $$

$$\eqalign{ & \mathop E\limits^ \to \left( {x,t} \right) = {E_0}\cos \left( {kx - \omega t} \right)\,\,{\widehat a_y} \cr & \mathop H\limits^ \to \left( {x,t} \right) = - {H_0}\cos \left( {kx - \omega t} \right){\widehat a_z} \cr} $$

$$\eqalign{ & \mathop E\limits^ \to \left( {x,t} \right) = {E_0}\cos \left( {kx - \omega t} \right)\,\,{\widehat a_y} \cr & \mathop H\limits^ \to \left( {x,t} \right) = - {H_0}\cos \left( {kx - \omega t - {\pi \over 2}} \right){\widehat a_z} \cr} $$