Final answer:
To express the frequency in inverse seconds when n changes from 4 to 3, calculate the period of the wave by taking the reciprocal of the frequency. For example, if the frequency is 264 Hz, the period would be 3.79 x 10^-3 s.
Step-by-step explanation:
The frequency can be expressed in inverse seconds when n changes from 4 to 3 by calculating the period of the wave. The period (T) is the inverse of frequency. So, we can calculate T by taking the reciprocal of the frequency. For example, if the frequency is 264 Hz, the period would be T = 1/264 Hz = 3.79 x 10-3 s = 3.79 ms.