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Trig identities?

  1. Apr 19, 2010 #1
    1. The problem statement, all variables and given/known data
    How to get from

    [tex]\sqrt{2+2cosx}[/tex]
    to

    2cos(x/2)

    3. The attempt at a solution

    I'm pretty much stuck on this.
    I can only see that is simplifies by taking out the common factor 2, which isnt correct.
     
  2. jcsd
  3. Apr 19, 2010 #2

    rock.freak667

    User Avatar
    Homework Helper

    Well id cos2x=2cos2x-1, then cosx=2cos2(x/2)-1
     
  4. Apr 20, 2010 #3
    Yup, thanks!
     
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