I reviewed the first drafts of HW 3, and here are some of my notes.

1) L1 and L2 are the distances from each speaker to the point of interest where we want to find the interference. Neither of these is equal to 4.5m in this case. See the textbook for some more tips.

2) A couple of errors I saw in this section:

See this page for more advice on problems 2 and 3.

For Problem 4, I would point to this page. Also, at least one person wrote that the initial frequency was 500Hz instead of 550Hz: watch out!