How to derive Mersenne's fundamental frequency formula?

[Mars Yeung]

I'm talking about equation 22,

Does anyone know how to derive this? It's Marin Mersenne's formula for fundamental frequency, but I'm perplexed as to how he derived it.

L would be the length, F would be force, and μ would be mass per unit length.
f is the frequency

Thanks

 

[fresh_42]

I don't know your source. Can you specify what is given to derive it from?