Questions relating to wave interference and beat frequency.

1. Two people are creating circular waves from a sound machine, at the same frequency. The
wave interference creates a pattern like the one shown above. The thicker lines represent
the crests and the thin lines represent the troughs. Determine whether constructive or
destructive interference happens at each indicated point.
A:
B:
C:
D:
Assume that an observer is located at (x,y)= (5,1) What would the path difference be?
Assume that the frequencies are now different, one at 536Hz and another at 543Hz. What is
the frequency that we hear? What is the beat frequency?