1. The problem statement, all variables and given/known data Prove for effective index N that n1<N<n2. 2. Relevant equations N=n1sin(theta) TIR is theta>thetacritical snells law-n1sin(theta)=n2sin(theta2) 3. The attempt at a solution I know why N is strictly less than n1 since sin(theta) goes from 0 to 1 and if its at 1 theta has to be 90. For TIR to actually happen N must be strictly less than n1. But I'm having trouble proving the n2<N part.