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Re: Something wrong with this integral (see text)

• To: mathgroup at smc.vnet.net
• Subject: [mg44603] Re: Something wrong with this integral (see text)
• From: "RFins" <rf31415 at hotmail.com>
• Date: Mon, 17 Nov 2003 03:38:38 -0500 (EST)
• References: <boif3m$oaf$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Well if you add the integrands you get an integral of Cos[L] which is
clearly NOT integrable over the positive real axis, and since integration is
a linear operator that means there is indeed a problem.  The first integral
is actually non-integrable.  regards,  RF

"Ihor Stealth" <stealth at gmx.net> wrote in message
news:boif3m$oaf$1 at smc.vnet.net...
> Hi All
>
> 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?
>
> Tnx for any help.
>
> Ihor
>
>
>