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MathGroup Archive 2004

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Re: RE: Trigonometric simplification - newbe question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49074] Re: [mg49031] RE: [mg49004] Trigonometric simplification - newbe question
  • From: DrBob <drbob at bigfoot.com>
  • Date: Wed, 30 Jun 2004 05:34:19 -0400 (EDT)
  • References: <200406290850.EAA18738@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

If you want to specify that n>0 is an even integer, you can do this:

expr =
    (4*(2*a*Sin[(n*Pi)/2] -
       a*Sin[n*Pi]))/
     (n^2*Pi^2);
even = expr /. n -> 2*k

(2*a*Sin[k*Pi] -
    a*Sin[2*k*Pi])/(k^2*Pi^2)

Simplify[even, {k \[Element] Integers, k > 0}]

0

Bobby

On Tue, 29 Jun 2004 04:50:08 -0400 (EDT), David Park <djmp at earthlink.net> wrote:

> Walter,
>
> Add an assumption to Simplify (In Version 5, at least).
>
> expr = (4*(2*a*Sin[(n*Pi)/2] - a*Sin[n*Pi]))/(n^2*Pi^2);
>
> Simplify[expr, n \[Element] Integers]
> (8*a*Sin[(n*Pi)/2])/(n^2*Pi^2)
>
> But I don't know how one would specify in the assumptions that n was an even
> integer greater than zero, say.
>
> David Park
> djmp at earthlink.net
> http://home.earthlink.net/~djmp/
>
>
>
> From: Christensen [mailto:fedderwi at uni-bremen.de]
To: mathgroup at smc.vnet.net
> To: mathgroup at smc.vnet.net
>
> Hi,
>
> 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?
>
> Thanks,
> Walter
>
> Trigonometric simplification - newbe question
>
>
>
>



-- 
DrBob at bigfoot.com
www.eclecticdreams.net


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