[填空题]
Two loudspeakers are 1.80cbv;prb:ozt3; obb58b/6le d m apart. A person stands 3.00 m fro.cne )-uklca (w6rs ng5mlfyt9 j)oi;-fh*u1m one speaker and 3.50 m h 6rcc g19s.) llmjuwun-;5 e(*io)f ta-kyfn 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
