Chapter 1, Problem 69P

Show that if you have three polarizing filters, with the second at an angle of $45.0°$to the first and at third at an angle of $90.0°$to the first, the intensity of light passed by the first will be reduced to 25.0% of its value. (This is in contrast to having only the first and third, which reduces the intensity to zero, so that placing the second between them increases the intensity of the transmitted light.)