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calculus

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verify the following identity
cos(x+y) + cos(x-y)=2cosxcosy

  • calculus - ,

    cos(a+b)=cos(a)cos(b)-sin(a)sin(b)
    cos(a-b)=cos(a)cos(b)+sin(a)sin(b)
    What happens when you add the two together?

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