Intensity

Two essential knowledge statements, and they sit in an unexpected place. EK 14.3.A.3.i: intensity is a measure of the amount of power transferred per unit area. EK 14.3.A.3.ii: the intensity of a wave is the average power per unit area over one period of the wave. Both hang off EK 14.3.A.3, which is about polarization reducing a wave's intensity, so the definition arrives in Topic 14.3 rather than in the periodic waves topic where you would look for it.

The treatment is qualitative. No intensity equation appears in the Waves, Sound, and Optics group of the AP Physics 2 sheet, and intensity has no entry in that group's symbol list. Malus's law is not in the CED. What is asked for is the reasoning: the same power through a smaller area is a higher intensity, and polarizing a beam removes power and so lowers it.

Amplitude, carefully. EK 14.1.A.6.iii says only that the energy a wave carries increases with increasing amplitude. The familiar claim that intensity goes as amplitude squared is not in the AP Physics 2 CED, so do not build an answer on it.

Where the inverse square shape comes from. A point source spreading into empty space spills its power over a sphere, whose surface area $4\pi r^2$ is printed in the sheet's geometry table. Fixed power divided by a growing area gives the inverse square fall off. The CED does not state this for waves, so treat it as geometry you can argue rather than a required relation.