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Homework Help: Real part of travelling wave

  1. Nov 18, 2012 #1
    1. The problem statement, all variables and given/known data

    A travelling wave f(x,t) = ei(kx -wt). Show that the real part of the wave can be written as cos(kx)cos(wt) + sin(kx)sin(wt)

    2. Relevant equations

    Euler e = cos(θ) + isin(θ)

    Also ei(θ12) = e1 . e2

    3. The attempt at a solution

    The - symbol is throwing me off and I can't find any examples to help me out. Does the second equation I gave above become e1 / e2? And then carry on and cancel out to get the answer?

    Any and all help appreciated thanks.
  2. jcsd
  3. Nov 18, 2012 #2


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    Science Advisor
    Homework Helper
    Gold Member

    I don't think that would help. Just leave the - sign in and apply Euler's formula.
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