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    Guys can someone help with the following question..
    From a point A, a boat sails due north for 7km to B. The boat leave point B and moves at a bearing of 100 degrees for 10km until it reaches C. Calculate the distance of C from A.

    I keep getting the wrong answer. This is my working out:

    SinC/7 = Sin100/10
    C= 43.6

    Therefore angle B is 180-(100+43.6)
    = 36.4

    AC/sin36.4 = 10/sin100

    AC = 10sin36.4 / sin100
    = 6.026 cm

    However 6.026 isn't the answer. The answer is 11.2.

    Where have I gone wrong??


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    (Original post by Taraah)
    SinC/7 = Sin100/10
    C= 43.6
    This first statement is not true.

    Draw a diagram.. You cannot do this question using the sine rule - you have no pairing angle and lengths.
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    The book tells me to use the cosine rule, but I still get the answer wrong. I've written the question exactly the way its written in the book. I drew a diagram but now I'm really confused


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    (Original post by Taraah)
    The book tells me to use the cosine rule, but I still get the answer wrong. I've written the question exactly the way its written in the book. I drew a diagram but now I'm really confused


    This was posted from The Student Room's iPhone/iPad App
    You should be able to work out the angle ABC by noting that angles on a straight line add up to give 180 degrees.

    Then use the fact that

    c^2 = a^2 + b^2 - 2ab\cos C
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    (Original post by Taraah)
    The book tells me to use the cosine rule, but I still get the answer wrong. I've written the question exactly the way its written in the book. I drew a diagram but now I'm really confused


    This was posted from The Student Room's iPhone/iPad App
    If you've drawn the sketch correctly you should have a value for a, b and an angle which (if the ship goes on a bearing of 100 from and the angle of a straight line is 180 what would be the angle inside the triangle?) http://gyazo.com/336ae70eb7cd08fc049fc564ef9c676b
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    note that bearings are measure from north, clockwise
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    Rearrange:

    Things to bear in mind (no pun intended):
    - Bearing are measured north clockwise meaning angle B has a measurement of 80 degrees.
    - Angles are opposite to sides.
    - Plug your numbers in using brackets and round.
    - Don't forget to square root your answer.
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    (Original post by Secret.)
    If you've drawn the sketch correctly you should have a value for a, b and an angle which (if the ship goes on a bearing of 100 from and the angle of a straight line is 180 what would be the angle inside the triangle?) http://gyazo.com/336ae70eb7cd08fc049fc564ef9c676b
    Hey thank you!! I drew the diagram incorrectly, thanks for helping i got the right answer now, finally!


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    (Original post by Secret.)
    If you've drawn the sketch correctly you should have a value for a, b and an angle which (if the ship goes on a bearing of 100 from and the angle of a straight line is 180 what would be the angle inside the triangle?) http://gyazo.com/336ae70eb7cd08fc049fc564ef9c676b
    Hey is it possible that you can help me with a another question:
    A helicopter flies on a bearing of 200 degrees from A to B, where AB= 70km. It then flies on a bearing of 150 degrees from B to C, where C is due south of A. Work out the distance of C from A.

    I properly know how to work it out, but I struggle with drawing the sketches.. Can you please tell me how to sketch would look like? Because I know I'm not drawing it right.


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    (Original post by Taraah)
    Hey is it possible that you can help me with a another question:
    A helicopter flies on a bearing of 200 degrees from A to B, where AB= 70km. It then flies on a bearing of 150 degrees from B to C, where C is due south of A. Work out the distance of C from A.

    I properly know how to work it out, but I struggle with drawing the sketches.. Can you please tell me how to sketch would look like? Because I know I'm not drawing it right.


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    Hi, sorry for the late reply, I'm guessing it would look something like: http://gyazo.com/78d9fa8f6386c96686a99cbe70af496d

    It also shows that C is due south of A
    hope this helps.
    (I kept the north lines so you can see how I got the drawing, the angles are not exact and don't have to be just approximate e.g. for 200 I used the north line as the angle of 180 and added approx 020 to it.
 
 
 
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