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Math Help - Trigonometry

  1. #1
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    Trigonometry

    The expression \frac{cosx-cos3x}{sen3x-senx} is equal the:

    a) -tgx

    b) -cotg2x

    c) tg2x

    d) cotg2x

    e) tgx
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  2. #2
    Eater of Worlds
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    What is this wacky notation?. I assume sen means sin and tgx mean tanx?.

    Going with that:

    \frac{cos(x)-cos(3x)}{sin(3x)-sin(x)}=\frac{2sin(x)cos(x)}{2cos^{2}-1}=\frac{sin(2x)}{cos(2x)}=tan(2x)
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  3. #3
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    Thank you very much
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