Question 615588
On a typical day at an ocean port, the water has a maximum depth of 18m at 6.00 a.m. The maximum depth of 9m occurs 6.8h later. Write an equation of the form h = a cos k(t-p) + q to describe the relationship between the depth of the water and time. 
I already determined the parts: a= 4.5, q= 13.5, p= 6 , but I have no idea how to get the k ( in the form of (2π\k).
Could possible give an explanation of how to get the k， please? Thank you~
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Period = (2pi)/k
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Period for you is 6.8 hr
2pi/k = 6.8
k= (2pi)/6.8
k = pi/3.4
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Cheers,
Stan H.