$ {z_1} = A\sin (kx - \omega \,t) $ , $ {z_2} = A\sin (kx + \omega \,t) $ , $ {z_3} = A\sin (ky - \omega \,t) $ .
Wave \({Z_2} = A\sin (kx + \omega t)\), is travelling towards negative \(x-\)direction.
Wave \({Z_3} = A\sin (ky - \omega t)\) is travelling towards positive \(y\) direction.
Since waves \(Z_1\) and \(Z_2\) are travelling along the same line so they will produce stationary wave.
$ {z_1} = A\sin (kx - \omega \,t) $ , $ {z_2} = A\sin (kx + \omega \,t) $ , $ {z_3} = A\sin (ky - \omega \,t) $ .