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Help 2004 Trig Q4bii

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  • 07-06-2009 6:38pm
    #1
    Foirfe
    Closed Accounts Posts: 18 ✭


    I hav the solution but still cant figure where there getting it
    I used x's instead of teta's

    2 cos x -7cos x/2 =0

    The part I don’t get is how they change the angles to x/2’s


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    #2
    ya-ba-da-ba-doo
    Closed Accounts Posts: 884 ✭✭✭ya-ba-da-ba-doo


    Logs... Let cosX= 2cos^2X/2 - 1...... CosX is the same as cos2(X/2)


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    #3
    Dmullar
    Closed Accounts Posts: 67 ✭✭Dmullar


    I Let X/2 = A

    So you get

    2Cos2A -7CosA = 0

    then use the identity given, (Cos2A = 2Cos^2(A) - 1) and factorise and change A back to X/2 at the end.


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