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Math Help - Sum and Difference formulae (sin and cos)

  1. #1
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    Question Sum and Difference formulae (sin and cos)

    I'm just curious about the,



    identities, is there a simple way to derive them?

    I have a test in a few days and I don't like memorizing too much.

    Thanks again!
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  2. #2
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    No simple way to derive them I'm afraid - more time and effort than you can afford to waste in a test.

    Just write them down and/or memorise them.

    \displaystyle \sin{(\alpha \pm \beta)} = \sin{\alpha}\cos{\beta}\pm\cos{\alpha}\sin{\beta}

    \displaystyle \cos{(\alpha \pm \beta)} = \cos{\alpha}\cos{\beta}\mp \sin{\alpha}\sin{\beta}.


    If I can memorise them you can too :P
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