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MathGroup Archive 2004

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Re: Trigonometric simplification - newbe question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49051] Re: Trigonometric simplification - newbe question
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Tue, 29 Jun 2004 04:50:39 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On 6/28/04 at 4:13 AM, fedderwi at uni-bremen.de (Christensen) wrote:

>this is a Mathematica newbe question for sure:

>Mathematica comes up with the following result:

>(4*(2*a*Sin[(n*Pi)/2] - a*Sin[n*Pi]))/(n^2*Pi^2)

>Now I have the additional assumption that n is element of {1,2,3,
>...) (and a is real)

>How do I tell Mathematica to take this into consideration and
>remove the Sin[n*Pi] term?

You can use Assumptions to specify your assumptions, i.e.

Simplify[(4*(2*a*Sin[(n*Pi)/2] - a*Sin[n*Pi]))/(n^2*Pi^2),
    Assumptions -> {n \[Element] Integers}]
    
which results in

(8*a*Sin[(n*Pi)/2])/(n^2*Pi^2)

But note the Sin[n*Pi] cannot be removed without additional assumptions since it evaluates to either -1, 0 or 1 for different intgers n.
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