The depth of the water at the end of a pier changes periodically along with the movement of tides. On
a particular day, low tides occur at 12:00 am and 12:30 pm, with a depth of 2.5 m, while high tides
occur at 6:15 am and 6:45 pm, with a depth of 5.5 m. Let t = 0 be 12:00 am.
Graph the equation d = -1.5cos 474 +4 that models the situation using a graphing calculator and
use it to answer the following questions.
How many times during this day is the depth at
the end of the pier equal to 4 meters?
A.2 times
B.3 times
C. 4 times
D.5 times
