Using Liouville's Theorem to Show that Bounded Entire Functions are Polynomials

In summary, the conversation discusses the condition for an entire function to be a polynomial of degree less than or equal to m. It involves an inequality |f(z)| ≤ M|z|m for all z such that |z| ≥ R, where f: ℂ → ℂ is an entire function. The conversation also considers the application of Liouville's theorem in this scenario. The suggestion is to consider the Taylor expansion for f and argue that for fixed radii, the function is bounded if the degree of the polynomial is greater than or equal to m.
  • #1
shebbbbo
17
0
Let f: ℂ→ ℂ be an entire function. If there is some nonnegative integer m and positive constants M,R such that

|f(z)| ≤ M|z|m, for all z such that |z|≥ R,

show that f is a polynomial of degree less that or equal to m.


im really lost on this question. i feel like because there is an inequality sign that i may have to use the ML inequality but I've tried that and i didnt get very far? am i going in the right direction?

any help or hints would be appreciated :-)

thanks
 
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  • #2
It seems like it may be an application of Liouville. Every time you have entire and bounded together, consider Liouville's theorem.

Maybe you can argue that for balls of fixed radius 1,2,3,.. |f| is bounded if the degree of the poly. is ≥ m, by , e.g., consider the Taylor expansion for f , which is global in ℂ , but let me think about it some more.
 

What is complex analysis?

Complex analysis is a branch of mathematics that deals with the study of functions in the complex number plane. It involves the use of techniques and concepts from calculus, such as derivatives and integrals, to analyze and understand complex functions.

What are complex numbers?

Complex numbers are numbers that have both a real and an imaginary part. They are typically written in the form a + bi, where a and b are real numbers and i is the imaginary unit (√-1). Complex numbers are important in complex analysis because they allow us to represent and analyze functions in the complex number plane.

What is a singularity in complex analysis?

A singularity is a point in the complex plane where a function is undefined or does not behave in a well-defined manner. It can be either a removable singularity, where the function can be extended to be defined at that point, or an essential singularity, where the function cannot be extended to be defined at that point.

What is the Cauchy-Riemann equation?

The Cauchy-Riemann equation is a set of two partial differential equations that must be satisfied by a complex function in order for it to be differentiable. It relates the real and imaginary parts of a complex function and is an essential tool in complex analysis.

What are some applications of complex analysis?

Complex analysis has many applications in mathematics, physics, engineering, and other fields. It is used to study and understand functions and equations in the complex plane, as well as problems involving fluid flow, electromagnetism, and quantum mechanics. It is also used in signal processing, image processing, and data analysis.

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