Given data:
* The fundamental frequency of the guitar string is f = 400 Hz.
Solution:
The frequency of the second overtone is,
[tex]\begin{gathered} f^{\prime}=3f \\ f^{\prime}=3\times400 \\ f^{\prime}=1200\text{ Hz} \end{gathered}[/tex]Thus, the frequency of the second overtone is 1200 Hz.
