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Math Help - Trig - Cosine

  1. #1
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    Trig - Cosine

    Explain why cos85 + cos95 = 0.

    --> cos 85 degrees + cos 95 degrees = 0.


    Thank you
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  2. #2
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    consider the problem as

     \cos(90-5)+\cos(90+5)

    use the compound angle identity keeping in mind that \cos(90) = 0
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  3. #3
    Super Member bigwave's Avatar
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    they cancel out to zero

    if you think about where 90degrees is
    you will see that the cos beween 0 to 90 (85) is the same length as the cos from 90 to 180 (95) just 5 degrees both sides of off 90degrees however in the I quadarent
    the cos is positive and in the II quadarant the cos neg so they cancel out to zero
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