Can Two Different Functions Have the Same Output for a Single Point?

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Discussion Overview

The discussion revolves around whether two different functions can yield the same output for a specific input point. Participants explore this question in the context of function definitions, domains, and the concept of bijections.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions if it is possible for two different functions, ##f## and ##g##, to satisfy ##f(p) = g(p)## at a point ##p## while remaining distinct, i.e., ##f \neq g##.
  • Another participant provides examples where different functions yield the same output at a specific point, such as ##f(x) = x^2## and ##g(x) = \sin(x)## at ##p=0##, suggesting that this scenario is common.
  • A further example is presented where ##f(x) = \frac{x^2 - 1}{x - 1}## and ##g(x) = x + 1## are equal for all points except at ##x = 1##, highlighting that differing domains can lead to functions being considered distinct despite similar outputs elsewhere.

Areas of Agreement / Disagreement

Participants express differing views on the implications of functions having the same output at a point while being distinct. There is no consensus on the broader implications of this scenario, as some examples suggest it is common, while others emphasize the importance of domain differences.

Contextual Notes

Participants note that the discussion hinges on the definitions of functions and their domains, which may affect the interpretation of when two functions can be considered the same or different.

kent davidge
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Today, while reading about bijections, a question came into my mind. And that is: is there any way that two different functions ##f## and ##g## acting on a same point ##p## gives the same output? In symbols, as I'm not good in English, is it possible that ##f (p) = g(p)## with ##f \neq g##?
 
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Oh and perhaps I should say I'm considering the same domain for the two functions.
 
kent davidge said:
Today, while reading about bijections, a question came into my mind. And that is: is there any way that two different functions ##f## and ##g## acting on a same point ##p## gives the same output? In symbols, as I'm not good in English, is it possible that ##f (p) = g(p)## with ##f \neq g##?
This happens all the time: ##p=0## for ##f(x)=x^2\; , \;g(x)=\sin(x)\; , \;h(x)=|x|## etc. However ##f=g## if ##f(p)=g(p)## for all points ##p \in \operatorname{dom}(f)=\operatorname{dom}(g)##. We also widely use the fact, that functions are the same at one point and close in their neighborhood, when we approximate a function by its tangent in ##p##.
 
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kent davidge said:
Today, while reading about bijections, a question came into my mind. And that is: is there any way that two different functions ##f## and ##g## acting on a same point ##p## gives the same output? In symbols, as I'm not good in English, is it possible that ##f (p) = g(p)## with ##f \neq g##?
Here's an example that's almost what you're talking about:
##f(x) = \frac{x^2 - 1}{x - 1}## and ##g(x) = x + 1##
f(x) = g(x) everywhere except at x = 1, the only point where f is not defined. Although the two functions have the same values almost everywhere, the domains are different (the domain of f doesn't include x = 1, and the domain of g is all real numbers), so they are different functions.
 
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