Water Depth Word Problem Modeled with Cosine Sine Function

Analyzing the time between high tides and the depth of the water, I make a function that models the tides and then calculate the safe hours for a ship to enter the port. At minute 13:27 I wrote the inverse cosine of .667 or arccos(.667), that should be arccos(-.667). Find free review test, useful notes and more at http://www.mathplane.com/ If you'd like to make a donation to support my efforts look for the "Tip the Teacher" button on my channel's homepage    / profrobbob