longitudinal waves have a crest or not ? I am not sure.
Think: what is the crest of a wave?
A wave is not a curved line... What is a wave? It is a travelling disturbance, periodic both in space and time. That disturbance can be the height of the water waves. There you see real crests and troughs. But it can be pressure, or electric or magnetic field, electric current or voltage, or displacement of a point on a string and a lot of other things. These quantities have maxima called "crest" and minima "trought" at certain positions and the distance between subsequent crests or troughs is the wavelength.
There are longitudinal and transversal waves, but all of them are some periodic disturbance with maxima and minima...
longitudinal waves have a crest or not ? >>> have/not have
he's telling you that ALL waves have alternating "crest" and "trough". by simple inference, longitudinal waves have "crest" and "trough" as well.
The policy of this place is that we do not give exact answers and full solutions. You get hints and have to find out the solution.
sorry, I'm not good in English. :!!)
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