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Math Help - trig equation

  1. #1
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    Cool trig equation

    Find all values of theta in the interval 0<theta<360

    2 cos^2 theta - 1=0
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  2. #2
    MHF Contributor Amer's Avatar
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    Quote Originally Posted by blame_canada100 View Post
    Find all values of theta in the interval 0<theta<360

    2 cos^2 theta - 1=0
    2\cos ^2 \theta -1 = 0

    \cos ^2 \theta = \frac{1}{2}

    \cos \theta = \mp \frac{1}{\sqrt{2}}

    theta equal the angle 45 in all quarters
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  3. #3
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    Hello blame_canada100
    Quote Originally Posted by blame_canada100 View Post
    Find all values of theta in the interval 0<theta<360

    2 cos^2 theta - 1=0
    Alternatively, you could use \cos2\theta = 2\cos^2\theta - 1

    So \cos2\theta = 0

    \Rightarrow 2\theta = 90^o,\,270^o,\,450^o,\,630^o

    Then divide by 2.

    Grandad
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