Proving Continuity of F:XxI->I with Continuous Functions

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Discussion Overview

The discussion centers on proving the continuity of the function F:X×I→I defined by F(x,t)=(1-t)f(x)+tg(x), where f and g are continuous functions from a topological space X to the unit interval I. The participants explore the implications of continuity in this context and seek to clarify the necessary steps to demonstrate F's continuity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant asks how to explicitly show that F is continuous, given the continuity of f and g.
  • Another participant mentions that the inverse image of an open set is open, suggesting a potential approach to the proof.
  • Some participants discuss the properties of continuous functions, noting that compositions, sums, and products of continuous functions are also continuous, but express uncertainty about whether this holds for arbitrary topological spaces.
  • A participant expresses a desire to understand the inverse image of specific intervals and considers trying a specific example to clarify their understanding.
  • Another participant suggests thinking about how sums and products are proven to be continuous, indicating that the continuity of F may not require extensive proof due to the properties of continuous functions.

Areas of Agreement / Disagreement

Participants generally agree on the continuity of F based on the properties of continuous functions, but there is some uncertainty regarding the applicability of these properties in arbitrary topological spaces. The discussion remains somewhat unresolved as participants explore different aspects of the proof.

Contextual Notes

Some participants express limitations in their understanding of continuity in arbitrary topological spaces, particularly regarding the continuity of sums and products outside of R^n. There is also a mention of needing to determine the inverse image of intervals, which remains unresolved.

Euclid
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How can I show that [tex]F:X\times I\to I[/tex] given by [tex]F(x,t)=(1-t)f(x)+tg(x)[/tex] is continuous, given that [tex]f:X\to I[/tex] and [tex]g:X\to I[/tex] are continuous (here I is the unit interval [0,1]). It seems that F is continuous, but I want to show that explicitly. Any help appreciated! X is any topological space.
(I wasn't sure what section to put this in - sorry!)
 
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The inverse image of an open set is open...
 
what do you know about continuous functions? compositions of them are still continuous, as are sums, products,...
 
mathwonk said:
what do you know about continuous functions? compositions of them are still continuous, as are sums, products,...
I'm willing to take that compositions of continuous functions are continuous without proof. I know that sums and products are continuous, but only when the domain is some subset of R^n. Does this carry over to any domain? If that's the case, then there is nothing to show.
I guess my main hangup is determining the inverse image of say (a,b). I'm going to try a specific example and see if that helps.
 
think about how you prove sums and products are continuous.

i.e. the addition and multiplication mapp from RxR to R are cotinuous. then if you have two continuous maps f:X-->R and g:X-->R you get one continuous map

(f,g):X-->RxR, and you comkpose with addition or multiplication. so it has nothing to do with the domain of the functions.

i agree there is nothing to do for your problem. but it can only be good to look at examples.
 

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