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MathGroup Archive 2005

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Re: Simplification question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg59085] Re: Simplification question
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Thu, 28 Jul 2005 02:27:33 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, U.K.
  • References: <dc76pp$jvg$1@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.
> 
Because it is a wrong answer!

In[1]:=
Simplify[Cos[m*Pi], Assumptions -> m \[Element] Integers]

Out[1]=
(-1)^m

In[2]:=
Simplify[Cos[m*Pi], Assumptions -> m \[Element] Integers] /. m -> 3*m

Out[2]=
(-1)^(3*m)

If m is even then

In[3]:=
Simplify[Cos[2*k*Pi], Assumptions -> k \[Element] Integers]

Out[3]=
1

If m is odd then

In[4]:=
Simplify[Cos[(2*k + 1)*Pi], Assumptions -> k \[Element] Integers]

Out[4]=
-1

Regards,
/J.M.


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