How Should I Calculate dr² in Differentiation: Directly or by Finding dr First?

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Discussion Overview

The discussion revolves around the differentiation of the expression $$r^2= \lambda^2(1+\frac{m}{2\lambda})^2$$ and the appropriate method for calculating $$dr^2$$. Participants explore whether to derive $$dr$$ first and then square it, or to differentiate $$r^2$$ directly.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether to find $$dr$$ first or to calculate $$dr^2$$ directly from $$r^2$$, indicating a lack of clarity in the differentiation process.
  • Another participant seeks clarification on the notation, differentiating between $$dr^2$$ and $$(dr)^2$$.
  • A participant suggests interpreting $$dr^2$$ as $$(dr)^2$$ and proposes a method involving solving for $$r$$, computing $$dr$$, and then squaring the result.
  • Further clarification is provided by referencing the context of $$dr^2$$ in the 3-sphere metric, although this does not resolve the differentiation question.
  • A participant presents two approaches to the problem, providing equations for both $$d(r^2)$$ and $$(dr)^2$$, leaving the choice of method open-ended.

Areas of Agreement / Disagreement

Participants express differing interpretations of the notation and methods for differentiation. There is no consensus on the best approach to calculate $$dr^2$$, and the discussion remains unresolved.

Contextual Notes

The discussion highlights ambiguity in notation and the differentiation process, with participants relying on different interpretations and approaches without reaching a definitive conclusion.

PhyAmateur
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In one physics problem if $$r^2= \lambda^2(1+\frac{m}{2\lambda})^2$$

what is ##dr^2 ?##

Should I find ##dr## starting from ##r= \lambda(1+\frac{m}{2\lambda})## first and then square or find ##dr^2## starting from r^2? I know this is a basic question in differentiation using chain rule but it seems I am stuck over this..
 
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A little more context would be helpful here.

Are you trying to find (dr)2 or dr2. I think there's a difference.
 
It is written as $$dr^2$$ I was just wondering if I should derive once and then after finding the answer, derive twice.. What do you say?
 
This notation is ambiguous to me. I can't advise you further without more information about this problem where you found it.
 
I would interpret ##dr^2## as ##(dr)^2##, not as ##d(r^2)##. The straightforward way is to solve for r, compute ##dr=\frac{dr}{d\lambda}d\lambda##, and then square the result.
 
It is the same $$dr^2$$ found in the 3 sphere metric for example..
 
PhyAmateur said:
It is the same $$dr^2$$ found in the 3 sphere metric for example..

##r^2 = λ^2(1 + \frac{m}{λ} + \frac{m^2}{4λ^2}) = λ^2 + mλ + \frac{m^2}{4}##

##r = λ(1 + \frac{m}{2λ}) = λ + \frac{m}{2}##

##\frac{d(r^2)}{dλ} = 2λ + m##

##d(r^2) = (2λ + m)dλ \ \ (A)##

##\frac{dr}{dλ} = 1##

##dr = dλ##

##(dr)^2 = (dλ)^2 \ \ (B)##

A or B, take your pick.
 

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