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Math Help - Trigonometric Equation

  1. #1
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    Trigonometric Equation

    Solve the trig equation..

    1-9*cos^2 (2x) = 0


    My Work:

    1-9*cos^2 (2x)
    cos^2 (2x) =1/9
    cos (2x) =1/3 or -1/3
    2x=arccos(1/3)
    x=0.5*arccos(1/3)
    or
    2x=arccos(-1/3)
    x=0.5*arccos(-1/3)

    Is this correct? When I plug the value of x into the given trig equation, I do not get 0 = 0.
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  2. #2
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    Re: Trigonometric Equation

    seems right to me
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  3. #3
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    Re: Trigonometric Equation

    what you've done is correct but not complete. There are actually 8 solutions between 0 and 2pi and of course there are an infinite number of solutions overall.
    Thanks from prasum, nycmath and topsquark
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