[填空题]
Two loudspeakers are 1.80 m apart. ce7qe- pr)t;*ro h6q4vhgg )bAq, 3u3tjvp5 mh person stands 3.00 m from one speaker and 3.3,ht mu35jq vp50 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
