A wave source generates circular waves that spread out from it on the surface of a pond. The wavelength of these waves is 6.00 cm. (a) At some instant a crest is passing point A, 18.0 cm east of the wave source. What part of the wave is passing point B, 25.5 cm to the north of the wave source, at this instant? (b) At this instant what is the phase dierence between points A and B? (c) A quarter of a cycle later what is the phase at each of points A and B?