Okej have a piece of glass with refractive index n2 and tickness t. A ray of light falls on the glass with the angle theta1 (from a medium with recrative index n1). In the glass the ray has the angle theta2 and when it exits it has now got the displacement d (compared with the ray that went from air to glass). Now show that the formula d=tsin(theta1)(1-(n1cos(theta1) / n2cos(theta2)) is correct. I know it is suppose to be simple trig, but the only thing i can even figure out to do is that 90-theta1 = theta ... then i'm stuck.. can't see how to connect anything. please give me some hints.