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Math Help - Difference between plus minus and minus plus

  1. #1
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    Difference between plus minus and minus plus

    In this page: LINK

    In the second yellow table, they have an equation

    Difference between plus minus and minus plus-capture.png


    Why exactly do they have different symbols, plus minus and minus plus?

    Does it mean that if the first sign is minus then the other has to be plus and vice versa?
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  2. #2
    Super Member TheChaz's Avatar
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    Re: Difference between plus minus and minus plus

    The sign inside the parenthesis is the OPPOSITE of the sign between terms.
    cos(x + y) = cos(x)cos(y) - sin(x)sin(y)

    So yes, it means what you said!
    Last edited by TheChaz; December 23rd 2011 at 04:14 AM.
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  3. #3
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    Re: Difference between plus minus and minus plus

    Quote Originally Posted by cosmonavt View Post
    Click image for larger version. 

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    Why exactly do they have different symbols, plus minus and minus plus?
    It is shorthand notation.
    When the first is plus the second is minus:
    \cos(x+y)=\cos(x)\cos(y)-\sin(x)\sin(y).

    When the first is minus the second is plus:
    \cos(x-y)=\cos(x)\cos(y)+\sin(x)\sin(y).
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  4. #4
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    Re: Difference between plus minus and minus plus

    Thanks guys!
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