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Re: Something wrong with this integral (see text)


"Ihor Stealth" <stealth at gmx.net> 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
convergence."

David Cantrell


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