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Homework Help: Use trig identities to prove

  1. Sep 17, 2007 #1
    [tex]\cos (t)=\cos(t+2\pi)[/tex]

    I know it is kind of silly, but I need to do it.

    I could have sworn that a sum formula would have worked, ie.,
    [tex]\cos(\alpha+\beta)=\cos \alpha \cos \beta -\sin \alpha \sin \beta[/tex]

    but when I sub in [tex]t[/tex] and[tex] 2\pi[/tex] for the RHS, I am getting [tex]-\cos t[/tex]

    Where did I go wrong....


    Edit: IDK why LaTex alpha isn't showing on RHS
    Last edited: Sep 17, 2007
  2. jcsd
  3. Sep 17, 2007 #2


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    Homework Helper

    What is cos (2 pi)? (You're gonna kick yerself...)

    P.S. One of the alphas wasn't displaying because you wrote "alpa"; the cos t didn't display because you left out a space between "cos" and "t"; TeX is unforgiving that way...
  4. Sep 17, 2007 #3
    Ouch! I did not know it was possible to kick myself there:cry: ...

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