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Math Help - Simple Trig Problem Which I Can't Seem To Get!

  1. #1
    Senior Member
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    Simple Trig Problem Which I Can't Seem To Get!

    Hey guys



    A lighthouse is 10 km north-east of a ship travelling due west at 16 km/h.

    i) How far is the ship from the lighthouse 45 min later?

    ii) What is the bearing of the light-house from the ship at this time?

    For i):

    I used the cosine side formula…

     <br />
LB^2 = 10^2 + 12^2 - 2(10)(12)cos45
    LB = 8.6 cm<br />

    Which is wrong because the answers say it’s 20.3 km.

    For ii):

    I used the cosine angle formula:

    cos \angle B = 55 degrees
    Bearing = 270 + 55
    =325 degrees T
    Which is also wrong according to answer (070 degrees T)

    Could someone please please show me how to do this question?
    Last edited by xwrathbringerx; April 22nd 2009 at 02:35 AM.
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  2. #2
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
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    Hello, xwrathbringerx!


    I made exactly the same mistake that you made! . . . LOL

    I too had my ship moving east !


    Gee, I hope no one saw that . . .
    .
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