Inequality and complex numbers

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SUMMARY

The discussion centers on proving inequalities involving complex numbers, specifically the expression |e^iz| under certain conditions. Participants clarify that for |z| >= 3, the parameter b must be less than or equal to 0, leading to the conclusion that |e^iz| is bounded by 1 when the imaginary part of z is non-negative. The conversation highlights the need for precise definitions of variables a and b, as well as the correct interpretation of complex magnitudes.

PREREQUISITES
  • Understanding of complex numbers and their properties
  • Familiarity with Euler's formula: e^(ix) = cos(x) + i*sin(x)
  • Knowledge of complex number magnitudes
  • Basic skills in mathematical proof techniques
NEXT STEPS
  • Study the properties of complex exponentials and their magnitudes
  • Learn about inequalities involving complex numbers
  • Review the implications of the imaginary part of complex numbers on their behavior
  • Explore advanced topics in complex analysis, such as contour integration
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Students studying complex analysis, mathematicians working with inequalities in complex numbers, and educators seeking to clarify concepts related to Euler's formula and complex magnitudes.

oddiseas
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Homework Statement

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

Homework 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 don't know where to go next.
 
Last edited:
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oddiseas said:

Homework Statement



Show that |e^iz|<=1 for Im(z)>=0
b)show that if |z|>=3 then the following inequality holds


Homework Equations





The Attempt at a Solution



|e^iz|=e^-b(cosa+isina)
and since the inmaginery part is always one, the magnitude is always less or equal to one' provided b is <=0. Now the second part i am having trouble with.

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.
 
Please post the exact problem you are supposed to solve. The following makes no sense:
oddiseas said:
b)show that if |z|>=3 then the following inequality holds
What following inequality? It doesn't appear in either your original post or the edited post.
 

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