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    Hey,

    I can't get my head around how they've solved this using the CAST diagram.

    cos x = -\frac {sqrt 3}{2}

    and x = 150

    so in the mark scheme it says clockwise rotation of 150 or anti-clockwise rotation of 210

    can someone explain this for me please?
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    (Original post by Ravster)
    Hey,

    I can't get my head around how they've solved this using the CAST diagram.

    cos x = -\frac {sqrt 3}{2}

    and x = 150

    so in the mark scheme it says clockwise rotation of 150 or anti-clockwise rotation of 210

    can someone explain this for me please?
    I'm not sure what you mean? There are two solutions, one where x=150^{\circ} and one where x = 360^{\circ} - 150^{\circ} = 210^{\circ}?
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    (Original post by Zacken)
    I'm not sure what you mean? There are two solutions, one where x=150^{\circ} and one where x = 360^{\circ} - 150^{\circ} = 210^{\circ}?
    Thanks for your reply and help.

    The bit where they got 360-150 to get 210. Why did you do this?
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    (Original post by Ravster)
    Thanks for your reply and help.

    The bit where they got 360-150 to get 210. Why did you do this?
    For Cos:
    If the first solution is say x(degrees) then the second solution is always 360 (degrees)-x.

    (Then the other solutions (if needed) are ±360 degrees the main 2 solutions above.)
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    The reason the above is true is that \cos x = \cos (2\pi - x) which is fairly obvious from the graph, but I'm not very familiar with the CAST stuff.
 
 
 
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