Answer:
Explanation:
D, the vertical shift, also called the sinusoidal axis, or the average value, can be calculated by averaging the y-value of the high point and the y-value of the low point: D = (6 + 2) / 2 = 4.
A, the amplitude, will be the difference of the high and low point y-values divided by 2: (6 - 2) / 2 = 2. We should also think of A as how far away the high and low points are from the average value, D.
Next, we calculate B, the parameter controlling the length of the period by using the formula: B = 2π / period. We are told the 1st high tide is at 4 am, while the 1st low tide is at 10 am. These are 6 hrs apart, which means the highs are 12 hrs apart. Thus, B = 2π / 12 = π/6.
Lastly, an unshifted cosine function will begin at a peak, when x = 0. This cosine function has a peak when time = 4, meaning it is shifted right by 4 from a normal cosine curve. So C = - 4.
Putting all together, we get the following:
x: time elapsed since midnight (in hrs)
y: depth of water (in ft)
y = 2cos(π/6(x - 4)) + 4.
If you wanted to give the answer in the form your teacher requested, distribute the B-value across (x - 4), though the form above is more commonly used.