In the wave equation, it states that wavelength = velocity of the wave ÷ frequency. Or is it the constant velocity of light 299,792,458 divided by the frequency. And if it is the velocity of the wave ÷ frequency, how do I find the velocity of the wave without knowing wavelength? All I know is frequency and the length of the string that is being plucked.
All oscillations (more explicitly standing waves) which can be excited in the string have wavelengths Lambda related to the string length L as
L = n * Lambda / 2
where n > 0 is arbitrary integer. Usually you need to calculate parameters of the lowest harmonic, so, you should take n = 1: