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Math Help - cos (x - y)

  1. #1
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    cos (x - y)

    When sin x = -8/17 and lies in quadrant 3 and cos y = -4/5 and lies in quadrant 2, find cos (x - y).
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  2. #2
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    Quote Originally Posted by magentarita View Post
    When sin x = -8/17 and lies in quadrant 3 and cos y = -4/5 and lies in quadrant 2, find cos (x - y).
     cos(x-y) = cos(x)cos(y) + sin(x)sin(y)
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  3. #3
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    Tell me.........

    Quote Originally Posted by Mush View Post
     cos(x-y) = cos(x)cos(y) + sin(x)sin(y)
    Tell me, what is the name of that formula?
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  4. #4
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    Re:

    That is one of the additional formulas .
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  5. #5
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    ok...

    Quote Originally Posted by mathaddict View Post
    That is one of the additional formulas .
    I understand. Thanks.
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