Uncovering the Origins of the Symbol 'r' in Mathematics

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Homework Help Overview

The discussion revolves around the origins and definitions of the symbol 'r' in mathematical contexts, particularly in relation to radial distance and resistivity in physics.

Discussion Character

  • Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the distinction between lower case 'r' as radial distance and upper case 'R' as resistance, questioning their usage in equations. There is an inquiry into the definition of resistivity and its relation to these symbols.

Discussion Status

The conversation has progressed with participants providing clarifications regarding the definitions and applications of 'r' and 'R'. Some guidance has been offered on the mathematical relationships involved, though no consensus has been explicitly stated.

Contextual Notes

There is an indication of confusion regarding the use of 'dR' in equations, suggesting that assumptions about the quantities involved may need further examination.

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Summary:: I have a question that I don't understand but you may know where r was come from.

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I mentioned about my question on the addition.
 
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Lower case ##r## is radial distance from the axis. Upper case ##R## is resistance. Two different quantities. Besides, you can't have ##dR## on both sides of the equation you are questioning.
 
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##R = {\rho\;l\over A} ## is for a flat sheet with thickness ##l##.
Here ##dR = {\rho \, dr \over A}## is for a tube with radius ##r## and thickness ##dr##. Its area ##A## is ##2\pi Lr##
 
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Okay I get it now. Thanks both of you for attention :)
 

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