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MathGroup Archive 2005

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Re: Simplification question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg59082] Re: [mg59032] Simplification question
  • From: Pratik Desai <pdesai1 at umbc.edu>
  • Date: Thu, 28 Jul 2005 02:27:17 -0400 (EDT)
  • References: <200507270525.BAA19953@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

snoofly 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 think the reason is simple as Cos[even*Pi]=+1 and Cos[odd*Pi]=-1
Hence your expression does not specify whether m is odd or even, hence 
Mathematica returns the expression unevaluated
Using a recent reply on a post we can try this

Simplify[Cos[(3*Pi*n)], Assumptions -> Mod[n, 2] == 1]
 >>-1
Simplify[Cos[(3*Pi*n)], Assumptions -> Mod[n, 2] == 0]
 >>1

Best regards

-- 
Pratik Desai
Graduate Student
UMBC
Department of Mechanical Engineering
Phone: 410 455 8134



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