In a small harbour, the depth of the water at high tide is 10m, and at low tide is exactly zero. The depth of water follows approximately simple harmonic motion with amplitude (A), 5m and time period (T), 12 hours. On one day, high tide is noon.

If d is the depth of the water above the mean depth (5m), write an equation of the form

, substituting the appropriate values for

and

.

Where,

is time.

I already know

and

or

but i am not sure what the question is asking me to do. Does it want me to make a function for time so that when you input a time of day it will return an appropriate value? I am not sure, any ideas anyone?

Thanks