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:

- Some people thought n=6, which was incorrect.
- Some used v=343m/s. This is the speed of a sound wave in air,
*not*the speed of a wave on a string like this. - One person referred to the formula v=√T/(m/L). This is indeed a true equation, but not helpful here.

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!