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MathGroup Archive 2005

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Re: Simplification question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg59092] Re: Simplification question
  • From: "David W. Cantrell" <DWCantrell at sigmaxi.org>
  • Date: Thu, 28 Jul 2005 02:27:58 -0400 (EDT)
  • References: <dc76pp$jvg$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

"snoofly" <snoofly at snoofly.com> wrote:
> Can someone explain this to me please.
>
> Clear[m]
>
> Simplify[Sin[3 m Pi], Assumptions -> m \[Element] Integers]
> 0
>
> Simplify[Cos[3 m Pi], Assumptions -> m \[Element] Integers]
>
> Cos[3 m \[Pi]]
>
> I'm not sure why Mathematica cannot deduce that the second simplification
> should be (1)^m.

I presume you meant to say (-1)^m. Anyway, Peter Pein recently posted a
nice way to handle this, in sci.math.symbolic:

In[1]:= Refine[TrigFactor[Cos[3 m Pi]], Element[m, Integers]]

Out[1]= (-1)^m

David


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