A ray of light enters the long side of a 45°-90°-45° prism and undergoes two total internal

Question:

A ray of light enters the long side of a 45°-90°-45° prism and undergoes two total internal reflections, as indicated in FIGURE 26-66.
In figure 26-66.

The result is a reversal in the ray's direction of propagation. Find the minimum value of the prism's index of refraction, n, for these internal reflections to be total.