Rouche's Theorem: Find Zeros of f(z)=z^9-2z^6+z^2-8z-2 Inside Unit Circle

  • Thread starter AcC
  • Start date
  • Tags
    Theorem
In summary, Rouche's Theorem is a mathematical principle used to determine the number of zeros of a complex polynomial function inside a given region. It states that by comparing a simpler function with the given function, the number of zeros will be the same. The function f(z) used in Rouche's Theorem is a complex polynomial function, and the unit circle region is a circular region on the complex plane with a radius of 1. To determine the number of zeros of f(z) inside the unit circle, we compare it with a simpler function, g(z), and use Rouche's Theorem to determine the number of zeros based on the number of zeros of g(z).
  • #1
AcC
8
0

Homework Statement


Find the number of zeros of the folowing polynomial lying inside the unit circle,
f(z)= z^9 - 2z^6 + z^2 - 8z - 2



The Attempt at a Solution


Rouche's Theorem says if f and g differentiable which contains a simple loop s and all points inside s.
if |f(z)-g(z)|<|f(z)| for all z=s(t)
then f and g have same zeros inside s.

which g(z) should I choose, -2z^6, or z^2 or -8z
how can I determine?
 
Physics news on Phys.org
  • #2
Try, -8z. In general, try the term with the highest coefficient...
 

FAQ: Rouche's Theorem: Find Zeros of f(z)=z^9-2z^6+z^2-8z-2 Inside Unit Circle

1. What is Rouche's Theorem?

Rouche's Theorem is a mathematical theorem that is used to find the number of zeros of a complex polynomial function inside a given region.

2. How does Rouche's Theorem work?

Rouche's Theorem states that if two complex polynomial functions have the same number of zeros inside a given region, then the two functions must have the same number of zeros in the entire region. This allows us to determine the number of zeros of a function inside a region by comparing it to a simpler function with the same number of zeros.

3. How is Rouche's Theorem used to find zeros?

To use Rouche's Theorem to find zeros, we need to choose two polynomial functions, f(z) and g(z), where f(z) is the original function we want to find zeros of, and g(z) is a simpler function with the same number of zeros inside the given region. Then, we compare the values of f(z) and g(z) at each point on the boundary of the region. If the absolute value of f(z) is greater than the absolute value of g(z) at all points on the boundary, then f(z) and g(z) have the same number of zeros inside the region and we can use this information to determine the number of zeros of f(z).

4. How do I apply Rouche's Theorem to the function f(z)=z^9-2z^6+z^2-8z-2?

In order to apply Rouche's Theorem to this function, we need to find a simpler function with the same number of zeros inside the unit circle. One possible choice is g(z)=z^9, as it has all its zeros at the origin, which is inside the unit circle. Then, we can compare the values of f(z) and g(z) at each point on the boundary of the unit circle, and if the absolute value of f(z) is greater than the absolute value of g(z) at all points, we can conclude that f(z) has 9 zeros inside the unit circle.

5. What is the significance of finding the zeros of a function with Rouche's Theorem?

Finding the zeros of a function is an important step in understanding the behavior and properties of the function. Rouche's Theorem allows us to determine the number of zeros of a function inside a given region without having to actually find the zeros, which can be a difficult and time-consuming task. This information can then be used to analyze and graph the function more accurately.

Similar threads

Replies
8
Views
2K
Replies
4
Views
1K
Replies
6
Views
2K
Replies
2
Views
6K
Replies
2
Views
2K
Replies
5
Views
2K
Back
Top