1. This document discusses equations for modeling the combination of two waves through superposition. It provides equations for calculating the resultant wave amplitude and intensity based on the individual wave amplitudes and their phase difference. 2. Conditions are described for obtaining constructive or destructive interference between the waves based on their relative phases. Maximum and minimum intensities can be calculated. 3. The document also discusses how the same principles can be applied to model interference patterns from double-slit diffraction, with equations provided relating slit separation, wavelength, and observation point to fringe spacing and intensity.