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Math Help - Trig equations?

  1. #1
    Junior Member
    Joined
    Jan 2008
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    53

    Trig equations?

    I have a quiz tomorrow but i don't really get it:

    1. Given 4cos x-2=cos x, solve for x, to the nearest degree, in the interval 0 < x < 360

    i got 3cosx-2=0 but i don't know what to do after that..

    and

    2. Solve 2cos ^2θ-cosθ=1
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  2. #2
    MHF Contributor
    Joined
    Sep 2008
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    West Malaysia
    Posts
    1,261

    trigo

    Quote Originally Posted by eh501 View Post
    I have a quiz tomorrow but i don't really get it:

    1. Given 4cos x-2=cos x, solve for x, to the nearest degree, in the interval 0 < x < 360

    i got 3cosx-2=0 but i don't know what to do after that..

    and

    2. Solve 2cos ^2θ-cosθ=1

    (1) 4 cos x - cos x = 2
    3 cos x = 2
    cos x = 2/3
    basic angle x = 48.19
    Note that cos x is positive , thus it can be either in the first quadrant or the fourth quadrant .
    therefore , x = 48
    or
    x = 360 - 48.19
    =311.81
    = 311

    (2) 2 cos^2 x - cos x -1 = 0
    ( 2 cos x + 1 ) ( cos x - 1 ) = 0
    cos x = - 1/2 or cos = 1

    use the same method to solve .
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