# Mystic Darkness

A uniform, horizontal beam of light is incident upon a quarter cylinder of radius $\displaystyle R$, and has a refractive index $\displaystyle\mu$. Starting at a distance $x$ from the front of the cylinder, the table is not illuminated.

Find the value of $\displaystyle x$ (in cm).

Details and Assumptions:

• $R = 5cm$
• $\mu = \frac{2}{\sqrt{3}}$
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