Answer:
1. Letter A indicates the crest.
2. Letter E indicates the wavelength.
3. Letter C indicates the trough.
Step-by-step explanation:
1. Determination of the the crest.
A crest is simply defined as a point on a wave where the displacement is maximum (i.e highest).
Considering the diagram given above, the point where the displacement is maximum is A. Therefore, A is the crest of the wave.
2. Determination of the wavelength.
The wavelength of a wave is simply defined as the distance between two successive crest or trough.
Obeserving the diagram above, we can see that E gives the distance between two successive crest. Therefore, E is the wavelength of the wave.
3. Determination of the trough.
A trough is simply defined as a point on a wave where the displacement is minimum (i.e lowest). Thus we can say that the trough is the opposite of the crest.
Considering the diagram given above, the point where the displacement is minimum is C. Therefore, C is the trough of the wave.