Argument Theorem - Complex Analysis

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SUMMARY

The discussion centers on evaluating the contour integral of the function (1/2πi) * [z^(n-1)] / [(3z^n) - 1] dz using the Argument Theorem. The initial attempt incorrectly counted the zeros of both the numerator and denominator, leading to an erroneous conclusion of -1. The correct application of the Argument Principle requires counting only the zeros of f(z) = 3z^n - 1, which has n zeros, while noting that f'(z) = 3nz^(n-1) must also be considered. The integral's value is determined by the difference in the number of zeros and poles, confirming the necessity of proper function differentiation in complex analysis.

PREREQUISITES
  • Understanding of complex analysis concepts, specifically the Argument Theorem.
  • Familiarity with contour integrals and their evaluation techniques.
  • Knowledge of zeros and poles in complex functions.
  • Ability to differentiate complex functions, particularly in the context of the Argument Principle.
NEXT STEPS
  • Study the Argument Principle in detail, focusing on its applications in complex analysis.
  • Learn about contour integration techniques, including Cauchy's Integral Theorem.
  • Explore the differentiation of complex functions, specifically the implications of f(z) and f'(z) in integral evaluations.
  • Practice evaluating contour integrals with varying degrees of complexity to solidify understanding.
USEFUL FOR

Students and professionals in mathematics, particularly those studying complex analysis, as well as educators seeking to clarify the application of the Argument Theorem and contour integration techniques.

Shay10825
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Homework Statement



Evaluate (1/2ipi)* contour integral of [z^(n-1)] / [(3z^n) - 1 ] dz

Homework Equations



I would assume you would have to use the Argument Theorem since this problem comes after the proof of the argument theorem in my book.


The Attempt at a Solution



z^(n-1) has (n-1) zeros
(3z^n) - 1 has n zeros

therefore the integral is equal to (n-1)-n = -1

Is this correct?

Thanks
 
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Yes, use the Argument Principle, but no, you did it incorrectly.

If you are integrating f'(z)/f(z), then count the zeros (n) and poles (none) of f(z) only, not f'(z). Also, if f(z)=3z^n-1, then f'(z)=3nz^(n-1) so don't forget to take the 3n into account.

I guess you are assuming the contour is a simple closed contour enclosing all the roots of f(z).
 

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