We went over homework problems.

We reviewed our results for traveling waves. Then we argued for and checked a trigonometric identity

sin(A) + sin (B) = 2 sin[(A+B)/2] cos[(A-B)/2],

which we used to look at some cases of superposition (adding of waves, sometimes also known as interference). In the case of the two waves traveling in the same direction, we looked into the conditions for "constructive interference" and those for "destructive interference."

Another case we examined was two waves (equal amplitude, wavelength and frequency) traveling in opposite directions. The result was a so-called standing wave.