E.g., if you really get 0.7297 in this example, think about what that means. It's the sine whose graph passes through the origin, so the function has the form a sin bx. The average water depth is 12 feet and y is the number of feet above or below that level at time t, measured in hours after midnight. If you glance at the graph of cosine, you will see that this happens when the cosine is applied to 2 . The actual depth of the water is 12 - 0.8 or 11.2 feet.
Low tide is halfway between, or one-half a period.
No calculation is necessary. Since the amplitude is 4, the smallest value of the function is -4. Thus at low tide the H 2 O level is 12-4 or 8 feet.