Does an Analytic Function Vanishing on a Disc Boundary Vanish Inside?

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Homework Help Overview

The discussion revolves around the properties of analytic functions, specifically addressing whether an analytic function that vanishes on the boundary of a closed disc also vanishes throughout the entire disc.

Discussion Character

  • Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the identity theorem for holomorphic functions and its implications for the problem. There is also consideration of the Cauchy Integral Formula and its relevance to the function's behavior on the boundary versus inside the disc.

Discussion Status

Some participants have offered references to the identity theorem and the Cauchy Integral Formula as potential avenues for understanding the problem. Others are reflecting on these suggestions and considering their implications.

Contextual Notes

There is uncertainty regarding the initial steps to take in addressing the problem, and participants are encouraged to revisit their notes for relevant theorems and formulas.

Metric_Space
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Homework Statement




If an analytic function vanishes on the boundary of a closed disc in its domain
, show it vanishes on the full disc

Homework Equations



CR equations?

The Attempt at a Solution



Not sure how to start this one.
 
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Hi Metric_space! :smile:

Have you seen the identity theorem for holomorphic functions. This says

If two holomorphic functions f and g on a domain D agree on a set which has an accumulation point c in D then f = g on all of D.

Did you see something like that? It would immediately give you the answer...
 
Interesting ...I'll reread my notes. Thanks!
 
Metric_Space said:
Interesting ...I'll reread my notes. Thanks!

You could also use the Cauchy Integral Formula, which is almost certainly in your notes even if micromass' theorem isn't.
 
Is it just as simple as applying the Cauchy Integral formula?

ie. it follows directly from the CIF?
 
Well, what does the Cauchy Integral Formula say? What if you take the integral to be around the boundary of that disk?
 

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