Question 1205129
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Use a cosine function to describe the height of the tides of the ocean if high tide raises 
the water level to 5 m at noon and low tide drops it down to 1 m at 4 p.m. Let t = 0 be 12 noon.
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<pre>
Mid-line is half the sum of the maximum and the minimum height  {{{(5+1)/2}}} = {{{6/2}}} = 3 meters.

The amplitude is half the difference of the maximum and the minimum height  {{{(5-1)/2}}} = {{{4/2}}} = 2 meters.

Since the cosine function has the maximum at 12 noon, which corresponds to t= 0, it means
that the shift of the cosine function is zero.


The half of the period of the cosine function is 4 hours from 12 noon (maximum height) 
to 4 p.m. (minimum height) - so, the period is 8 hours.


Now we have everything to write the cosine function for the water level

    h(t) = {{{2*cos(2*pi*t/8)}}} + 3  meters.
</pre>

Solved.