Calculating (dr)^2: Formula & Examples

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Discussion Overview

The discussion revolves around the expression for \((dr)^2\) in the context of differential geometry and vector calculus, specifically examining different formulations and interpretations of the notation used. Participants explore theoretical aspects and mathematical representations related to this concept.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants question whether \((dr)^2\) is equivalent to \(dx^2 + dy^2 + dz^2\) or to \(\frac{(xdx + ydy + zdz)^2}{x^2 + y^2 + z^2}\).
  • One participant clarifies that if \(r\) is defined as \(r = \sqrt{x^2 + y^2 + z^2}\), then the second formulation may be correct.
  • Another participant inquires if the first expression refers to \((d\vec{r})^2\).
  • There is a suggestion that participants should clarify the notation before delving into questions.
  • One participant raises a question about whether \(r\) represents a radius or a metric/distance.
  • A participant explains that \(\mathbf{dr}\) is a differential position vector in 3D space, represented in Cartesian coordinates, and prompts others to consider the result of dotting this vector with itself.

Areas of Agreement / Disagreement

Participants express differing views on the correct formulation of \((dr)^2\), and there is no consensus on which expression is accurate or preferred.

Contextual Notes

Participants have not fully defined all terms and notations used, which may affect the clarity of the discussion. There are unresolved assumptions regarding the definitions of \(r\) and the context of the expressions.

Who May Find This Useful

This discussion may be of interest to those studying differential geometry, vector calculus, or related fields in mathematics and physics, particularly in understanding the nuances of differential notation and its applications.

jk22
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I'm confused, Is the value of ##(dr)^2##
$$dx^2+dy^2+dz^2$$

Or $$\frac{(xdx+ydy+zdz)^2}{x^2+y^2+z^2}$$

?
 
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What is ##r##? If it is ##r= \sqrt{x^2 + y^2 + z^ 2}##, then the second option is correct.
 
The first were ##(d\vec{r})^2## ?
 
Maybe you should tell what all that notation means before asking questions...
 
Is ##r## a radius or a metric / distance?
 
I think you meant that ##\mathbf{dr}## is a differential position vector between 2 closely neighboring locations in 3D space. In Cartesian coordinates, $$\mathbf{dr}=\mathbf{i_x}dx+\mathbf{i_y}dy+\mathbf{i_z}dz$$What do you get when you dot this vector with itself?
 

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