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Homework Help: Deriving Lagrange's Trig Identity (real part of a complex number in exponential form)

  1. May 12, 2010 #1
    1. The problem statement, all variables and given/known data
    I did the question with help, but did not understand why did we multiply e^-i(x/2)
    How do I know what to multiply for getting the real part of a complex number in exponential form?


    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. May 12, 2010 #2

    Mark44

    Staff: Mentor

    Re: Deriving Lagrange's Trig Identity (real part of a complex number in exponential f

    You need to give us more information. I don't know what problem you're trying to solve.
     
  4. May 12, 2010 #3
    Re: Deriving Lagrange's Trig Identity (real part of a complex number in exponential f

    http://mathforum.org/library/drmath/view/64574.html

    instead of using euler's formula i multiply by e^-(x/2)/e^-(x/2)
    after letting z=e^ix

    I am sorry I was in a rush at school.
     
  5. May 13, 2010 #4

    Mark44

    Staff: Mentor

    Re: Deriving Lagrange's Trig Identity (real part of a complex number in exponential f

    Show us what you're doing and where you're getting stuck.
     
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