What's so special about functions?

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Discussion Overview

The discussion revolves around the nature of functions and their significance in mathematics, particularly in algebra and calculus. Participants explore the distinction between functions and other types of relations, providing examples and questioning the reasons for the prominence of functions in mathematical study.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant references Larson's precalculus textbook, noting that a function assigns exactly one output for each input, and questions what other relations exist that do not adhere to this rule.
  • Another participant provides the equation of a circle as an example of a relation that is not a function, as it does not yield a unique output for every input.
  • It is suggested that functions possess many useful properties, which may explain their central role in mathematics, although the historical reasons for this focus are not fully explored.
  • Examples of important relations that are not functions include equality, inequality, and geometric relationships like parallelism and perpendicularity.
  • A participant discusses how functions naturally arise in physical contexts, such as tracking distance over time while driving, emphasizing the uniqueness of outputs for given inputs in such scenarios.
  • Another participant asks for examples of relations with multiple outputs for a single input, prompting a response that defines a relation where one input can relate to two outputs, such as the square root function.

Areas of Agreement / Disagreement

Participants express varying viewpoints on the importance of functions versus other relations, with some agreeing on the natural occurrence of functions in physical applications, while others raise questions about the existence and modeling of relations with multiple outputs. The discussion remains unresolved regarding the overall significance of functions compared to other relations.

Contextual Notes

Participants mention various types of relations and their properties, but there are limitations in the exploration of why functions are prioritized in mathematics, and the discussion does not resolve the implications of these different relations.

JamesGold
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In Larson's precalculus textbook, he says
A function from a set A to a set B is a relation that assigns to each element in the set A exactly one element in the set B. The set A is the domain (or set of inputs) of the function f, and the set B contains the range (or set of outputs).
This seems to imply that there are other relations for which this restriction need not hold. My first question is: what are some examples of such relations? And second, if there are other relations out there, then why are functions so important? Why are they what is primarily studied in algebra and calculus?
 
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A common example of an important equation that isn't a function would be the formula for a circle or something like y^2 + 3x = 6, since you cannot solve for a unique y.

I think the importance of function can turn into a very long and large post. I think it should suffice to say that functions have a lot of very handy and interesting properties. I'm not a historian, so I can't tell you exactly why functions became the main focus in a lot of mathematics. I can say that once you begin to really study functions you can say a lot about them and find out a lot more about other mathematical ideas, and maybe, if there is no other reason, that's why we choose to focus on them so much.
 
Last edited:
JamesGold said:
In Larson's precalculus textbook, he says



This seems to imply that there are other relations for which this restriction need not hold. My first question is: what are some examples of such relations? And second, if there are other relations out there, then why are functions so important? Why are they what is primarily studied in algebra and calculus?

Important examples of relations are of course the equality relation =, the not-equality relation ≠, the inequalities <,>,≤,≥. We also have the relation "is parallel to" or "is perpendicular to" between straight lines. Most of these relations are not functions and are very important in mathematics.

One of the most important reasons for studying functions is, I guess, that they arise naturally in physical applications. For example, let's say that I drive my car on the highway. When I start driving, I start my stopwatch. So at time 0, I am at my starting position. After 10 minutes, I might be 5 miles from my starting position. After 1 hour, I might be 20 miles from my starting position.
The key is that after a certain time t, I am a certain number of miles from the start. So I get a function in a very natural manner: at a certain time I can't be 10 and 20 miles from my starting position, this is impossible. So for each time, I can associate a unique distance that I am from the start. So I have a function.
As such, functions arise in a very natural manner. Furthermore, functions are really easy to handle.
 
I see - that makes sense. Are there any examples of relations where a given input can have two different outputs? Does this model anything?
 
JamesGold said:
I see - that makes sense. Are there any examples of relations where a given input can have two different outputs? Does this model anything?

Sure, for example: define xRy if x=y2. Then 1R1 and 1R(-1), so 1 is in relation with exactly two other numbers. In general, if x≥0, then xR\sqrt{x} and xR(-\sqrt{x}).
 

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