Two waves with frequencies f1 and f2 are superimposed. What formula gives the beat frequency f_B?

1. The beat frequency equals the absolute difference between the two original frequencies. 2. In formula form, this is f_B = |f1 - f2|, matching option B. 3. Option A instead adds the frequencies together, which is not how beat frequency is defined. 4. Options C and D describe an average and a product, neither of which is the beat frequency formula. _Source: OpenStax Physics (CC BY 4.0), Ch 14 "Sound", section Resonance and Beats_