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Math Help - double or half angle formula to solve

  1. #1
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    double or half angle formula to solve

    don't know how to use double or half angle formula to solve the equation:

    sin2x+cosx=0

    in the interval [0, 2pi) and the answers are pi/2, 7pi/6, 3pi/2, 11pi/6
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  2. #2
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    Quote Originally Posted by guardofthecolor4ever View Post
    don't know how to use double or half angle formula to solve the equation:

    sin2x+cosx=0

    in the interval [0, 2pi) and the answers are pi/2, 7pi/6, 3pi/2, 11pi/6
    Substitute \sin (2x) = 2 \sin x \cos x.

    Now factorise the resulting expression. Now apply the null factor law to get two simple trig equations that you need to solve over the given interval:

    \cos x = 0

    2 \sin (x) + 1 = 0
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  3. #3
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    thanks!
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