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Math Help - Trig Half-Angle Formula question

  1. #1
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    Trig Half-Angle Formula question

    Trig Half-Angle Formula question-bill004.jpg
    Can anyone find my mistake in the above work. My book gives a different answer for the above question. The first line in the above is given by the book.
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  2. #2
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    For starters, in the region \displaystyle \pi < \theta < \frac{3\pi}{2}, you should know that \sin{\theta} < 0,\cos{\theta} < 0 and \tan{\theta} > 0.

    So check your starting values of \sin{\theta} and \cos{\theta}.
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