\magnification=\magstep2


$$
  y(x, t) = A \cos(kx - \omega t + \phi)
$$


$$\eqalign{
  y_1(x, t) &= A_1 \cos(kx - \omega t)  \cr
  y_2(x, t) &= A_2 \cos(kx - \omega t + \phi) \cr
}
$$



\bye
