(1)(i) From the image, we can know the wavelength, the elapsed time, the waveform shown in the figure repeats for the third time, then the period, the wave velocity v= 20m/s(3 minutes).

(2) Although the propagation direction of the wave is uncertain, it can be determined that the waveform at this time is shown as a dotted line because it is =1.5t.. (2 points)