Chapter 1 - Functions and Limits - 1.3 New Functions from Old Functions - 1.3 Exercises - Page 43: 27

$D(t)=7.0+5.0 cos[\frac{2π}{12} (t−6.75)]$

The average depth is 7.0. The amplitude of the graph is 5.0. The period is 12 hours. A high point occurs at 6:45 am, which is 6.75 hours after midnight. We can use these values to write a function that models the depth: $D(t)=7.0+5.0 cos[\frac{2π}{12} (t−6.75)]$