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MathGroup Archive 2005

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Re: TrigExpand - Odd behavior

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55428] Re: TrigExpand - Odd behavior
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Wed, 23 Mar 2005 05:34:39 -0500 (EST)
  • References: <200503220851.DAA23768@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On 22 Mar 2005, at 09:51, Bob Stagat wrote:

>
> Try executing the following three lines and explain the last result...
>
> Cos[45 Degree]
>
> Cos[x+45 Degree]
>
> Cos[x+45 Degree]//TrigExpand
>
> Thanks...
> ~ BS ~
>
>
There is nothing wrong and nothing to explain. What you get is the 
expansion of iof Cos[x+45 Degree]  in terms of Sin[x], Cos[x], Sin[1 
Degree], Cos[1 Degree]. What else did you expect? You can see that the 
answer is correct by substituting  a numerical value for x as follows:


Chop[(Cos[x+45 Degree]//TrigExpand)/.x->45 Degree//N]


0


Chop[(Cos[x+45 Degree]//TrigExpand)/.x->15 Degree//N]


0.5

which is as it should be.

Andrzej Kozlowski


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