General definition of a derivative

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Discussion Overview

The discussion revolves around the general definition of a derivative in calculus, specifically the limit definition involving delta notation. Participants explore the implications of this definition and clarify notation used in mathematical expressions.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant presents the limit definition of a derivative as f'(x) = \lim_{\Delta x \rightarrow 0} \frac{\Delta y}{\Delta x} and questions why it cannot be applied when \Delta y approaches 0.
  • Another participant explains that since the function is y = y(x), it is more natural to consider the limit with respect to the variable x.
  • A participant expresses confusion regarding the notation f(x) = y and y(x) = y, questioning the meaning of these expressions and noting a potential mix-up.
  • One participant comments on the use of notation in mathematics and physics, suggesting that there may be an abuse of notation, particularly among physicists.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the notation and the application of the derivative definition. There is no clear consensus on the confusion surrounding the notation or the implications of the limit definition.

Contextual Notes

There are unresolved questions about the appropriateness of applying the limit definition in certain contexts and the clarity of notation used in mathematical expressions.

cscott
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I was told that the general definition of a derivative is

[tex]f'(x) = \lim_{\Delta x \rightarrow 0} \frac{\Delta y}{\Delta x}[/tex]
(supposed to be delta y over delta x, but I can't make the latex work :mad:)

but why can't it work when [itex]\Delta y \rightarrow 0[/itex]?
 
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Because the function is [itex]y=y(x)[/itex],so it's natural to consider the limit on the "x" (variable's) axis.


Daniel.
 
Oh, alright.

Another thing, what is f(x) = y or y(x) = y in normal notation? I thought f(x) replaced y, but the fuction y = y doesn't make sense, does it? I mixed up :frown:
 
Last edited:
Abuse of notation,i don't know how much mathematicians do it,but physicists adore it.

Daniel.
 

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