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Math Help - yet another trig identity...

  1. #1
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    yet another trig identity...

    these are getting me mad...

    Please help me on this one:

    Establish the identity:

    cos(\alpha+\beta) + cos(\alpha-\beta) = 2\cos\alpha\cos\beta

    Thanks in advance for your help!
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  2. #2
    MHF Contributor
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    What identities are you allowed to apply to this exercise?

    Thank you!
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  3. #3
    A riddle wrapped in an enigma
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    Quote Originally Posted by jpman View Post
    these are getting me mad...

    Please help me on this one:

    Establish the identity:

    cos(\alpha+\beta) + cos(\alpha-\beta) = 2\cos\alpha\cos\beta

    Thanks in advance for your help!
    Hi jpman,

    This is pretty straight forward if you use the sum and difference formulas of cosine.

    \cos(\alpha \pm \beta)=\cos \alpha \cos\beta \mp \sin \alpha \sin \beta
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  4. #4
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    Quote Originally Posted by masters View Post
    Hi jpman,

    This is pretty straight forward if you use the sum and difference formulas of cosine.

    \cos(\alpha \pm \beta)=\cos \alpha \cos\beta \mp \sin \alpha \sin \beta

    Dude, you rock.

    I totally missed the sum and difference formulas...

    Thanks a bunch!
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