Physics Study Guide/Standing waves
Standing waves[edit]
Wave speed is equal to the square root of tension divided by the linear density of the string.

Linear density of the string is equal to the mass divided by the length of the string.

The fundamental wavelength is equal to two times the length of the string.
Variables
λ: wavelength (m) 
Definition of terms
Tension (F): (not frequency) in the string (t is used for time in these equations). Units: newtons (N) 
Fundamental frequency: the frequency when the wavelength is the longest allowed, this gives us the lowest sound that we can get from the system.
In a string, the length of the string is half of the largest wavelength that can create a standing wave, called its fundamental wavelength.