Calculus: Early Transcendentals 8th Edition

$D(t) = 7.0+5.0~cos[\frac{2\pi}{12}~(t-6.75)]$
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: $D(t) = 7.0+5.0~cos[\frac{2\pi}{12}~(t-6.75)]$