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Homework Help: 1 of 2 killer questions-Trig

  1. Aug 18, 2005 #1
    1 of 2 killer questions--Trig

    suppose the depth of the tide in a certain harbor can be modeled by y=21-5cos(pi t)/6, where y is the water detph in feet and t is the time in hours. Consider a day in which t=0 represents 12:00 midnight. For that day, when are the first high tide and the first low tide and what is the water depth at each time?

    I came up with:
    High tide: 7 am, 16 feet; low tide 13 noon, 15 feet.

    That is wrong.....can anyone help? :confused:
  2. jcsd
  3. Aug 18, 2005 #2


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    Homework Helper

    [tex] \cos 0 = 1[/tex]
    [tex] \cos \pi = -1[/tex]
    Do not double post.
    Viet Dao,
  4. Aug 18, 2005 #3
    It's really qouit simpel you acctuaelly want to know when cos(pi*t/6) equals 1 and -1 (max and min). After you have done this you only have to find y for the calculated values of t. The answeres I got this way where: high tide at 6AM and 6PM with 26 feet and low tide at midnigth and noon with 16 feet.
  5. Aug 18, 2005 #4
    The light is shining....thank you
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