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Math Help - Solving trigonometric equations

  1. #1
    Newbie
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    Exclamation Solving trigonometric equations

    Hi,

    I have the solve the following equation without using a calculator:

    2cos2x=1+cosx, where x is in radians and between 0 and 2 pi.

    I used the double angle formulae to get that:

    (4cosx +3)(cosx -1)=0,

    But how can I figure out what cosx = -3/4 is?

    Con somebody help me? Is there an easier way of doing it? Any help is very much appreciated.
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  2. #2
    Math Engineering Student
    Krizalid's Avatar
    Joined
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    Santiago, Chile
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    Alas, you won't be able to find that by hand, there's where the calculator comes handy.

    There are certain angles easily found, but this is not the case.
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