[填空题]
Two loudspeakers are 1.8lo3wb y9tj;1pfsa,.pd) a) xn0 m +mkoc2g ig3ie06x c0f apart. A person stands 3.00 m from one speaker and 3.50 m from the otg02cc3+ 6i kieg 0mofxher.
(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
