Consider the image below:
Let $\theta_2$ be the angle between the axes of transmission of Polarizer 2 and Polarizer 3 and $\theta_3$ be the angle between the axes of transmission of Polarizer 3 and Polarizer 4.
Derive $I_4$, in terms of $I_2$, $\theta_2$ and $\theta_3$.
Any idea how to do this one?

