Confusion on a simple integration

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    Confusion Integration
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Discussion Overview

The discussion centers on the integration of the function ## \int dx/(x^2 + a^2)^{1/2} ##, particularly examining the case when ## a = 0 ##. Participants explore the implications of this limit and the resulting expressions, questioning the validity of different interpretations of the integral.

Discussion Character

  • Mathematical reasoning, Debate/contested

Main Points Raised

  • One participant presents the integral and its evaluation, noting that for ## a = 0 ##, the expression leads to two different logarithmic forms depending on the interpretation of the square root.
  • Another participant references a source indicating that the integral formula is only valid for ## a > 0 ##, suggesting a limitation in the original claim.
  • There is a reiteration that ## log(2x) ## and ## log(x) ## differ only by a constant of integration, implying that the two forms are equivalent in the context of indefinite integrals.
  • A later reply expresses gratitude for clarification, indicating that the discussion has been helpful in resolving confusion.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the validity of the integral when ## a = 0 ##, as there are competing views regarding the applicability of the formula and the interpretation of the results.

Contextual Notes

The discussion highlights potential limitations regarding the conditions under which the integral formula is applicable, particularly the dependence on the parameter ## a ## and the interpretation of the square root in the context of integration.

rude man
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TL;DR
Confused on integrating ## \int dx/(x^2 + a^2)^(1/2)##
The tables and Wolfram Alpha say
## \int dx/(x^2 + a^2) ^{1/2} = log~ [( x^2 + a^2)^{1/2} + x] ##.

So if a=0 we get as answer
## log (x + x) = log( 2x) ## if ## (x^2)^{1/2} = x, or
## log (x - x) = log( 0) ## if ## (x^2)^{1/2} = -x

but surely ## \int dx/(x^2)^0.5 = \int dx/x = log x ## ?

Only 2 roots of ##x^2 ## right?
 
Last edited:
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My list of integrals (Wikipedia) allows this formula only for ##a>0##.
 
log(2x) = log(2) + log(x), so log(2x) and log(x) differ only by a constant of integration.
 
phyzguy said:
log(2x) = log(2) + log(x), so log(2x) and log(x) differ only by a constant of integration.
Thank you a lot phyzguy! Could have driven me batty who knows for how long!
 

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