This is College Physics Answers with Shaun Dychko. The minimum angle at which reflected light will be polarized is called the Brewster's angle. And we have equation for it that says a tangent of the Brewster's angle is the index of refraction of the second material divided by index refraction of the first material. So, in this case we have light incident on some diamond and so light is traveling through an initial material with index refraction of 1.00 that of air and then is reflecting from diamond which has an index of refraction of 2.419. And then we're trying to figure out what is this <i>theta b</i> here such that the reflected light is polarized. So, take the inverse tangent of both sides and we have Brewster's angle then it’s the inverse tangent of <i>n two</i> over <i>n one</i>. So, the inverse tangent of 2.419 divided by one which is 67.5 degrees.