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Re: Re: Thx for your help

• To: mathgroup at smc.vnet.net
• Subject: [mg23787] Re: [mg23743] Re: Thx for your help
• From: Jack Goldberg <jackgold at math.lsa.umich.edu>
• Date: Sat, 10 Jun 2000 02:59:34 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

Hi,

Replace Abs[x] by 2x UnitStep[x]-x.  Mathematica knows the integral of 
x*UnitStep[x] and gets the correct answer in form of a UnitStep,

	-x^2/2+x^2*UnitStep[x]

which, if you factor the x^2/2 yields the answer below.

jack


On Mon, 5 Jun 2000, Jens-Peer Kuska wrote:

> Hi, since Mathematica don't know that
> 
> x^n*DiracDelta[x]== 0 /; n>0
> 
> it can't find that Integrate[Abs[x],x]-> x^2*Sign[x]/2
> 
> As book advice *not* a Mathematica book, a mathematics book
> seems to be more use full.
> 
> Regards
>   Jens
> 
> Jos\151 Mar\155a Lasso wrote:
> >
> > Hi,
> > Thx for the answers to my last post, but I have a new question, similar to
> > the last one, when I try: Integrate[Abs[x],x], there is no result, just the
> > original input, what I am doing wrong?, I need some advice about a good
> > book about Mathematica for beginers.Thx again.Best regards
> >
> > Jose M Lasso
> 
>