What's the Difference Between dx*dy and a Point?

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Discussion Overview

The discussion revolves around the conceptual differences between "dx times dy" and a point, exploring their mathematical and geometric interpretations. Participants delve into the nature of differentials, points, and their respective roles in mathematics, particularly in the context of calculus and geometry.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest that "dx times dy" refers to the differential of area, distinguishing it from a point, which is a geometrical object.
  • Others clarify that "dx" and "dy" represent infinitely small changes in their respective directions, leading to an infinitesimal area rather than a point.
  • A participant emphasizes that a point is an algebraic object, while "dx dy" is an algebraic expression related to limits and integrals.
  • There is a request for a definition of a point, with one participant suggesting it is an indivisible amount of space, while another describes it as an element of a vector space.
  • One participant notes that "dx*dy" cannot be visualized as a geometric object but should be understood in the context of mathematical processes like Riemann sums.
  • A later reply mentions LeBesgue's definition of a point, asserting that it clarifies the distinction between the differential area and a point, although it requires a certain mathematical background.

Areas of Agreement / Disagreement

Participants express various interpretations of both "dx times dy" and a point, indicating that multiple competing views remain. The discussion does not reach a consensus on the definitions or implications of these concepts.

Contextual Notes

Some participants' definitions depend on specific mathematical frameworks, and there are unresolved questions regarding the nature of points and differentials, particularly in relation to visualization and abstraction.

CaptainJames
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What's the difference between dx times dy and a point? Having trouble thinking about this... it's been hurting my head, any help would be greatly appreciated.
 
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What is the context of the question? "dx times dy" might be the "differential of area". It is, in any case, a differential which doesn't have anything to do with a point.
The question seems to me to be a lot like asking "What is the difference between the number 5 and a point?":confused:
 
No, I mean an infinitely small change in the x direction times an infinitely small change in the y direction.
 
it would be an infinitely small change in the area enclosed by a curve(s) in a plane. a point is just a point.
 
A point is a geometrical object. dx dy is an algebraic object.
 
Hmm, could someone define a point for me... i think the problem is that I define a point as an indivisible amount of space, which is probably wrong, any help?
 
A point is an element of a particular vector space (or, roughly, number system), for example R2
 
A point is an abstraction invented by Euclid.

dx*dy cannot be "visualized" as if it were a geometric object. Instead, visualize what one does with it, in context. Doing 2d integrals? Visualize finite partitions of a region (perhaps a grid of widths ΔxΔy), their Riemann sums under a function f, and the limiting behavior of all that. dx*dy is an informal way of saying we're looking at some limiting behavior, of finite Δx*Δy. Infinitesimals don't exist on their own - they exist with reference to some limiting process we're describing. Thus dx*dy has more mathematical meaning then just the 'point' at which it is located.
 
I see my problem, I was trying to apply my world to mathematics too readily, thanks for the help everyone.
 
  • #10
I guess a point can be considered a geometric shape with n sides and area, perimeter and volume =0 like a triangle with one null angle...
 
  • #11
LeBesgue's definition of a "point" is, as far as I am concerned, the best
conceptualisation of this abstract object. The downside is that it requires a
certain mathematical background. He stills manages to make the difference between
the differential area dx*dy and a point quite clear though.
 
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