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Homework Help: Inequality and complex numbers

  1. Sep 17, 2009 #1
    1. The problem statement, all variables and given/known data

    b)show that if |z|>=3 then the following inequality holds

    2. Relevant equations

    |z|>=3 now for this to hold b must be <=0 which gives the following:
    |e^iz|=e^b(cosa+isina) and taking the magnitude yeilds (e^2b)^1/2
    I dont know where to go next.
    Last edited: Sep 17, 2009
  2. jcsd
  3. Sep 17, 2009 #2


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    Science Advisor
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    Gold Member

    You are having trouble with the first part. What are a and b? Are you writing
    z = a + ib. If so, you should say so.

    This equation |e^iz|=e^-b(cosa+isina) can't be correct because you have a real number on the left and a complex number on the right.

    The "inmaginery" (that's imaginary) part of what is one? And why is it 1? Do you know how to compute the magnitude of a complex number?

    "provided b is <=0". You are given Im(z) >= 0.

    Back to the drawing board.
  4. Sep 17, 2009 #3


    Staff: Mentor

    Please post the exact problem you are supposed to solve. The following makes no sense:
    What following inequality? It doesn't appear in either your original post or the edited post.
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