hi, i know that the entry ray of light into a medium will exits parrallel to the entry ray. The problem ask me to prove it. i have drawn a diagram and done the mathematical calculation. i just can't put it into words, could some one please help me out. and 2nd part to that question is Derive an expression for the offset of the entry and exiting rays if the thickness of the sheet is T and the ray enters at an angle of incidence of θ. aaaaaahhh....im so stress out..because of this simple question.