I'm studying for the IB Physics HL exam, and I came across a question neither my physics teacher or I can solve. It has a diagram like so:
The text of the question is this:
A person wearing polarizing sunglasses stands at the edge of a pond in bright sunlight. The surface of the pond is flat and the line of sight of the person makes an angle theta with the surface. The refractive index of the pond water is $n$. What is the value for theta for which the intensity of the sunlight reflected by the surface to the person's eye a minimum?
The answer is $\arctan\left(\dfrac1n\right)$, and I'm not sure how to even really start.
I think I'm missing a key formula, but I don't know what.