Parallel polarization means field lies in the XZ-plane (y=0) that is the plane of incidence, the figure illustrates the case of parallel polarization
then the incident and reflected fields is given by
now the reflected wave is
let’s find out then by using the equation , .
and the transmitted fields in the second medium is
as and also that the tangential components of and are continuous at the boundary z=0.
from EQN (1)