Complex Analysis: Entire Function Series

Click For Summary
SUMMARY

The discussion focuses on proving that the series \(\sum_{n=1}^{∞}[1−\cos(n−1z)]\) is entire. Participants emphasize the need to demonstrate differentiability across the entire domain. The suggested approach involves using the ratio test and expanding the cosine function into a power series to analyze the convergence of the summed series. This method is confirmed as a valid strategy for establishing the entire nature of the function.

PREREQUISITES
  • Understanding of complex analysis concepts, specifically entire functions.
  • Familiarity with power series expansions, particularly for trigonometric functions.
  • Knowledge of convergence tests, including the ratio test.
  • Basic skills in differentiability within the context of complex functions.
NEXT STEPS
  • Study the properties of entire functions in complex analysis.
  • Learn how to apply the ratio test to series of complex functions.
  • Explore power series expansions for trigonometric functions, focusing on cosine.
  • Investigate the implications of differentiability in complex domains.
USEFUL FOR

Students and professionals in mathematics, particularly those specializing in complex analysis, as well as educators seeking to deepen their understanding of entire functions and series convergence.

tarheelborn
Messages
121
Reaction score
0

Homework Statement


I need to prove that \sum_{n=1}^{∞}[1−Cos(n−1z)] is entire.

Homework Equations





The Attempt at a Solution


I know that I need to show that the series is differentiable for its whole domain, but I am not sure how to do that. Should I try to use the ratio test?
 
Physics news on Phys.org
You probably mean 1-cos(z/n). Yes, expand the cos in a power series and try to say something about the convergence of the summed series using the ratio test.
 
Oops, that is what I mean. Thank you very much.
 

Similar threads

Replies
3
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
Replies
3
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 17 ·
Replies
17
Views
3K