Uncovering Unknown Functions: Solving for f(x) and g(x) in Complex Equations

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Discussion Overview

The discussion revolves around finding two unknown functions, f(x) and g(x), that satisfy the equations f(g(x))=|sin(x)| and g(f(x))=sin^2(sqrt(x)). Participants explore approaches to solving this problem, including the validity of guessing and the implications of function domains.

Discussion Character

  • Exploratory
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that guessing might be necessary to find suitable functions, proposing f(x)=sqrt(x) and g(x)=sin^2(x) as potential solutions.
  • Another participant questions the correctness of the proposed domains for the functions.
  • A participant expresses interest in finding an algorithm for more complex cases, indicating that simplifications can complicate the problem further.
  • Some participants assert that there are no general techniques for solving functional equations, emphasizing the nature of the problem as distinct from numerical equations.
  • There is a light-hearted acknowledgment that the method of "solution by inspection" is often perceived as mere guessing, yet it is recognized as a valid approach in mathematics.
  • Trial and error is defended as a valid mathematical practice, though some note it may not always be the most efficient method.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of guessing as a method for finding functions, with some supporting it and others emphasizing the lack of general techniques for functional equations. The discussion remains unresolved regarding the best approach to take.

Contextual Notes

Participants note that the domains of the functions may have been incorrectly stated, and there is a recognition that more complex examples could require different strategies, highlighting the limitations of the current discussion.

Kerbox
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Say you get a problem like this:
Find f(x) and g(x) when f(g(x))=|sin(x)| and g(f(x))=sin^2(sqrt(x)),
and Domain_f=R, Domain_g=[0,-> >

How would you approach to solve this, or do you have to keep guessing until you find two functions that fits?
 
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Kerbox said:
Say you get a problem like this:
Find f(x) and g(x) when f(g(x))=|sin(x)| and g(f(x))=sin^2(sqrt(x)),
and Domain_f=R, Domain_g=[0,-> >

How would you approach to solve this, or do you have to keep guessing until you find two functions that fits?

You'll have to keep guessing until you see:
f(x)=sqrt(x)
g(x)=sin^2(x)
Are you sure about the domains?
 
I was looking for an algorithm or something that would work, when the example wasnt as simple as this one. When a lot of simplifying had been done to the expressions for example.

And of course, the domains are reversed. Sorry about that.
 
No, there are no general solve-all techniques for functional equations
(where your unknowns are functions, rather than some numbers, for example)
 
arildno said:
No, there are no general solve-all techniques for functional equations
(where your unknowns are functions, rather than some numbers, for example)

Of course mathematicians don't want to be perceived as just guessing at possible answers so they have termed this method "solution by inspection." :biggrin:
 
geometer said:
Of course mathematicians don't want to be perceived as just guessing at possible answers so they have termed this method "solution by inspection." :biggrin:

:biggrin::biggrin::biggrin::biggrin::biggrin:
 
Hey, trial and error is a perfectly valid mathematical method! Of course it's not always the most efficient path to a solution. :-)
 
Tide said:
Hey, trial and error is a perfectly valid mathematical method! Of course it's not always the most efficient path to a solution. :-)
Well, it's a perfectly valid praxis, don't know about method though..:wink:
 

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