Posted by **Jillian** on Wednesday, August 22, 2012 at 4:34pm.

What would the values of A, B, and C be in this problem?

The tides in a particular bay can be modeled with an equation of the form d= A cos (Bt) + C, where t represents the number of hours since high-tide and d represents the depth of water in the bay. The maximum depth of water is 36 feet, the minimum depth is 22 feet and high-tide is hitting every 12 hours.

- Calculus -
**Reiny**, Wednesday, August 22, 2012 at 4:46pm
max - min = 36-22 = 14

so the amplitude is 7

what do we have to add to 7 to get 36 ? ----- 29

period of cosine curve = 2π/k

12 = 2π/k

k = π/6

so **d = 7 cos (πt/6) + 29**

check:

at t=0 , d = 7cos 0 + 29 = 36 ---> high tide

at t=3 , d = 7cos π/2 + 29 = 29 ---> makes sense

at t=6 , d = 7cos π + 29 = -7+29 = 22 ---> low tide

at t=9 , d = 7cos 3π/2 + 29 = 29 --->makes sense

at t=12, d = 7cos 2π + 29 = 7(1)+29 = 36 ---> back to high tide

- Calculus -
**Jillian**, Wednesday, August 22, 2012 at 4:54pm
What will the graph look like for two full periods?

- Calculus -
**Reiny**, Wednesday, August 22, 2012 at 5:06pm
first period:

mark off from 0 to 12, with marks at 0, 3, 6, 9, and 12

at 0 , d=36

at 3, d= 29

at 6, d = 22

at 9, d = 29

at 12, d = 36 --- end of first period, now repeat that

draw a smoth cosine curve .

(I am somewhat surprised you even asked that question)

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