Answer:
The possible frequencies are 525 Hz and 521 Hz
Step-by-step explanation:
A string must be tune in the same frequency with the note to eliminate beats.
Given;
Frequency of note C = 523 Hz
The frequency that the piano is been tune to = 523 Hz
The beat frequency heard = 2 beats /s.
The frequencies that must have been heard can be an addition of the beat or the reduction of the beat added to the string frequency.
Frequencies of the string = ± 523 Hz
= 521 Hz or 525 Hz
Therefore the frequencies of the string are 523 Hz and 521 Hz