1. The problem statement, all variables and given/known data A light ray is incident on a flat piece of glass with index of refraction n. Show that if the incident angle θ is small, the emerging ray is displaced a distance d = tθ(n - 1)/n form the incident ray, where t is the thickness of the glass and θ is in radians. 2. Relevant equations n1sinθ1 = n2sinθ2 3. The attempt at a solution Using Snell's law, right triangles, sin(a-b) identity, and small angle approximation, I have got it to: d = tθ(n-(cosθ/cosθR))/n [θR is angle of refraction in glass] how do I get cosθ/cosθR = 1?