I am trying to derive the Fresnel equations for the E field perpendicular to the plane of incidence. There is one transformation, I assume involves some general math, that I am having a mental blank on. It can be found here http://physics.tamuk.edu/~suson/html/4323/prop-em.html if you scroll down to Equation 7.17, they simply state that combining it with Equation 7.14 you can achieve 7.18, the fresnel equation. I assuming this is just some substitution and re araging but for the life of me I am unable to figure out how they did. it. Enlighten me. ________ Cummings BSc: Photonics BEng: Telecommunications and Internet Technologies.