Question

crest is the point where​

Answer 1

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Actually Welcome to the Concept of the Oscillations.

In a wave, when it's passing through two dimensions, then we can say that it has the periodic motion with a pattern, that can be anything, like

1.) Sinosudal wave

2.) Square wave

3.) Triangular wave

4.) Saw-tooth wave.

All these wave have a wavelength, which contains a Crest and trough.

==> Now, Basically a Crest is a point where the maximum or the peak value of the displacement perpendicular to the propagation of wave takes place in the positive direction.

==> Trough , are those points where the minimum value of displacement takes place in the direction perpendicular to the wave propagation in the Negative direction.

Answer 2

Explanation:

A crest is a point on a surface wave where the displacement of the medium is at maximum.