# Thread: Writing a Sinusoidal Function?

1. ## Writing a Sinusoidal Function?

Write a cosine function that models the oscillation of Eastport’s tides if their amplitude is 9 feet 8 inches, the equilibrium point is 12 feet 3 inches, the phase shift is -2.68 hours, and the period is 12.34 hours.

How exactly do I do this? I've only written Sinusoidal functions for charts of data where you can find the amplitude by diving the difference by 2 and whatnot. Could anybody solve this for me and explain it preferably!

2. ## Re: Writing a Sinusoidal Function?

Originally Posted by glambeth
Write a cosine function that models the oscillation of Eastport’s tides if their amplitude is 9 feet 8 inches, the equilibrium point is 12 feet 3 inches, the phase shift is -2.68 hours, and the period is 12.34 hours.

How exactly do I do this? I've only written Sinusoidal functions for charts of data where you can find the amplitude by diving the difference by 2 and whatnot. Could anybody solve this for me and explain it preferably!
$y = A\cos[B(x+C)]+D$

w/ what was given (and no other pertinent info) ...

$A = 9.67$

$B = \frac{2\pi}{12.34}$

$C = -2.68$

$D = 12.25$