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MathGroup Archive 2005

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Re: Simplify problems for checking easy equalities...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg53858] Re: Simplify problems for checking easy equalities...
  • From: "David W. Cantrell" <DWCantrell at sigmaxi.org>
  • Date: Tue, 1 Feb 2005 04:08:09 -0500 (EST)
  • References: <cti5nd$8n2$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

cyruserik at tele2.se (Cyrus Erik Eierud) wrote:
> Please Help!
>
> Thanks for all great answers I've already found here!
> My problem is that I can not simplify what to me seems as a very
> simple equality task. This is what I want Mathematica to return zero
> for:
>
> in[1]:= FullSimplify[Log[x^n] - n*Log[x]]
>
> out[1]= -n Log[x] + Log[x^n])
>
> I have used Simplify to check equalities, but the one above (and many
> other equations similar to the one above) just don't simplify. Am I
> doing anything wrong or does anyone know of a better way to check
> equalities?

That expression is not necessarily zero, and that, of course, is why
Mathematica will not simplify the expression as you wish. However, if you
supply appropriate conditions, so that the expression is necessarily zero,
then you should be able to get the desired simplification. For example,

In[2]:= Simplify[Log[x^n] - n*Log[x], x > 0 && Element[n, Reals]]

Out[2]= 0

David Cantrell


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