Is the symbol dx equivalent to Δx in these situations?

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Discussion Overview

The discussion revolves around the symbols dx and Δx, exploring their meanings and equivalences in the context of differential equations and physics. Participants examine whether these symbols can be used interchangeably in various scenarios, particularly in relation to speed and changes in position.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that Δx represents an actual finite difference, while dx signifies an infinitesimal difference.
  • One participant asserts that Δx = xfinal - xinitial is correct, but dx = xfinal - xinitial is incorrect.
  • Another participant questions whether the equations v = Δx/Δt and v = dx/dt can be considered equivalent under conditions of linear movement without force.
  • It is noted that while v = dx/dt is always correct, v = Δx/Δt requires specification of a particular interval.
  • A participant mentions that in physics and engineering, Δx is commonly used to denote a finite change, which is often used before transitioning to derivatives.

Areas of Agreement / Disagreement

Participants express differing views on the equivalence of dx and Δx, with some agreeing on their distinct meanings while others explore conditions under which they might be treated similarly. The discussion remains unresolved regarding the interchangeability of these symbols in various contexts.

Contextual Notes

Participants highlight the need for clarity in specifying intervals when using Δx, indicating a potential limitation in understanding the contexts in which these symbols apply.

karkas
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I have seen the symbol dx in differential equations, but recently I saw it appear in various other equations that I previously thought included Δx instead of dx.

Are those two symbols the same? I mean, is Δx = dx = xfinal - xinitial ?

This may be the wrong thread, but I am still a newcomer, and plus I thought I saw another such question around here before!

Thanks
 
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Welcome to PF!

karkas said:
I have seen the symbol dx in differential equations, but recently I saw it appear in various other equations that I previously thought included Δx instead of dx.

Are those two symbols the same? I mean, is Δx = dx = xfinal - xinitial ?

Hi karkas! Welcome to PF! :smile:

∆x is an actual difference.

dx is an infinitesimal difference.

dx/dt = lim{∆x(t)/∆t} = lim{[x(t+∆t) - x(t)]/∆t}.

(for linear functions, of course, it makes no difference)

So Δx = xfinal - xinitial is correct :smile:

but dx = xfinal - xinitial is wrong :cry:
 
Thanks Tiny - tim!

Yet I still don't understand something (probably it's because we're taught everything in Greek and I am still not adept with English terminology).

If I say that the speed is v = Δx/Δt and v = dx/dt is the same thing if there is no force disrupting the linear movement?
 
karkas said:
Thanks Tiny - tim!

Yet I still don't understand something (probably it's because we're taught everything in Greek and I am still not adept with English terminology).

If I say that the speed is v = Δx/Δt and v = dx/dt is the same thing if there is no force disrupting the linear movement?

hmm … mathematical symbols should be an international language! :smile:

Yes, v = dx/dt is always correct …

but if there's no acceleration, then v = ∆x/∆t is also correct.

However, when you write dx/dt, you don't need to explain it,

but when you write ∆x/∆t, you need to specify a particular interval. :wink:
 
In physics and engineering, cap delta is frequently used to denote a finite change, a little bit of something. Thus cap delta x denotes a finite change in x.

It is common in setting up a problem to write things in terms of finite differences before passing to the limit when these differences, in the form of ratios, become derivatives.
 

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