[填空题]
Two loudspeakers are gh33.ezw6shrm(st ,h x;8 zhr h9icw :go)(/vz7 l tpr1.80 m apart. A person stands 3.00 m from one speaker and 3.7z/vg t)rlo( p50 m from the other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f = Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$ Hz $\approx$ Hz
