Complex analysis question I don't understand solution

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Homework Help Overview

The discussion revolves around a complex analysis problem involving the mapping of a certain domain applied to a function. Participants are examining the conditions under which the real part of a complex variable, Re(w), is less than 1, particularly in the context of a specific function definition.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to understand the reasoning behind the condition Re(w) < 1, questioning whether it follows directly from the values of Re(w) being 1/2 and 0. Other participants discuss the criteria involving u < 0 and how transformations affect these conditions.

Discussion Status

Participants are actively engaging with the problem, exploring different interpretations of the criteria involved. Some guidance has been offered regarding the transformations and their implications, but there is no explicit consensus on the reasoning behind the conditions being discussed.

Contextual Notes

There are references to specific criteria such as u < 0 and transformations like z -> 1/w and z -> z + 1, which are central to the discussion but may not be fully understood by all participants. The original poster expresses confusion about the application of these criteria.

Genericcoder
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So I am self studying complex analysis using some notes online so here he is trying to figure the map of certain domain applied to a function I follow everything but the end I don't get in the end when he got Re(w) < 1 how did he get that ? is it just because Re(w) which is 1/2 and 0 in this case is always less than 1? or what I don't get it.

f(S) = {w ∈ C : |w −1/2| > 1/2, Re(w) < 1}.
 

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Notice at the beginning of the 3rd page, the first criteria given is u<0 which was kind of neglected until the end.
 
but why exactly 1 ? I don't see how would that make it the case... ? @ Mentallic

Perok ?
 
Genericcoder said:
but why exactly 1 ? I don't see how would that make it the case... ? @ Mentallic

Because u<0 which is Re(1/w)<0 was one of the criteria we found that needs to be true after we did the inversion z->1/w, but then we needed to do an expansion z->2z, and u<0 simply becomes u<2(0) which is still u<0, so nothing changes in that step while the circle did change. The final step is a translation of z->z+1 so if u<0 then this becomes u<0+1=1. Hence, Re(w)<1.
 
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Thank you makes sense.
 

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