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MathGroup Archive 2003

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Re: Something wrong with this integral (see text)

  • To: mathgroup at
  • Subject: [mg44436] Re: Something wrong with this integral (see text)
  • From: "David W. Cantrell" <DWCantrell at>
  • Date: Sun, 9 Nov 2003 06:01:24 -0500 (EST)
  • References: <boif3m$oaf$>
  • Sender: owner-wri-mathgroup at

"Ihor Stealth" <stealth at> wrote:
> I calculated two expressions:
> FullSimplify[Integrate[(-L^2)/(L^2 + 1)*Cos[L], {L,0, Infinity}]]
> and
> FullSimplify[Integrate[(-1)/(L^2 + 1)*Cos[L], {L,0, Infinity}]]
> They gave the same result, but in the first expression when we take
> L->Infinity, it's impossible to take integral, but MAthematica CAN do
> that.
> What the explanation of this?

This question was posted, separately, by Ihor to sci.math, where it has
already been thoroughly answered.

In short, at least in version 5: The two integrals do not give the same
result, and for the first integral, Mathematica says "Unable to check

David Cantrell

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