text: Waves varying sinusoidal in time, with period  are considered. That is
  where  is the amplitude,  is the wave height,  is the angular frequency and  is the wave phase. Consequently, also  in Eq. () has to be a sine wave, e.g.  with  a constant.
  Applying these forms of  and  in Eq. () gives:
  which is Greens law'.