Help light through a prism!!!?

Question

Find alpha mas , the largest value of the angle alpha such that no light is refracted out of the prism at face AC if the prism is immersed in air.
Express your answer in degrees. Ignore any reflections from the surface BC.
here's the link to the picture
http://i54.photobucket.com/albums/g99/ca...
Light is incident along the normal to face AB of a glass prism of refractive index 1.58 , as shown in the figure.

Answer 1

Find the place in the book where it tells about total internal reflection. Because the incident light is normal to to face AB, there is no refraction at that point.

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