Argument Theorem - Complex Analysis

In summary, the contour integral of [z^(n-1)] / [(3z^n) - 1 ] dz is equal to -1, using the Argument Principle and taking into account the zeros and poles of f(z) only. It is also important to consider the factor of 3n when calculating f'(z). The contour should be assumed to be a simple closed contour enclosing all the roots of f(z).
  • #1
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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  • #2
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).
 

FAQ: Argument Theorem - Complex Analysis

What is the Argument Theorem in Complex Analysis?

The Argument Theorem, also known as the Argument Principle, is a theorem in complex analysis that relates the values of a complex function inside a closed curve to the number of zeros and poles of the function inside the curve. In other words, it allows us to determine the number of zeros and poles of a complex function within a region without explicitly finding them.

What is the significance of the Argument Theorem?

The Argument Theorem is significant because it provides a powerful tool for analyzing the behavior of complex functions. It allows us to determine the number of zeros and poles of a function within a given region, which can help us understand the structure of the function and make predictions about its behavior.

How is the Argument Theorem used in practice?

The Argument Theorem is commonly used in the field of complex analysis to study the properties of complex functions. It can be used to determine the number of zeros and poles of a function within a region, to find the range of values of a function, and to prove the existence of solutions to certain equations.

Can the Argument Theorem be applied to all complex functions?

No, the Argument Theorem can only be applied to analytic functions, which are functions that can be represented by a convergent power series. This means that the function must be differentiable at all points within the region of interest.

Are there any limitations to the Argument Theorem?

Yes, the Argument Theorem has some limitations. It can only be applied to functions that are analytic in a given region, and it does not provide any information about the exact locations of the zeros and poles of a function. Additionally, it only applies to closed curves, so it cannot be used for functions that have singularities outside of a closed curve.

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