1. The problem statement, all variables and given/known data 2. Relevant equations Snell's Law n1sin(theta_1)=n2sin(theta_2) Total Internal Refraction: sin(theta_c)=(n_2/n_1) lambda_n=lambda_n 3. The attempt at a solution So I drew the triangle and this is what I got, and well here is just a picture so far of what I have. I've done this problem before and got n=(theta)-(arcsin((sin(theta)/n)) and from there I have no idea. But I did a different approach. Any ideas. I've tried differentiating implicitly after that and trying to integrate and just got a huge mess.