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MathGroup Archive 2005

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Re: Re: TrigExpand - Odd behavior

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55458] Re: [mg55441] Re: TrigExpand - Odd behavior
  • From: DrBob <drbob at bigfoot.com>
  • Date: Thu, 24 Mar 2005 03:41:59 -0500 (EST)
  • References: <200503231034.FAA04048@smc.vnet.net>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

>> I just thought that it is frustratingly complex for
>> something that can be written so simply and which
>> Mathematica will, in fact, obtain if you tickle it
>> in just the right way

So tickle it the right way.

TrigExpand is intended to EXPAND expressions. Don't be surprised if it doesn't give you the simplest possible answer.

Bobby

On Wed, 23 Mar 2005 05:34:52 -0500 (EST), <stagat at linkline.com> wrote:

> Thanks for all your comments.
>
> Yes, I realize that the lengthy expression provided by Mathematica is correct.
> Perhaps a better example of the result I'd hoped to see is given by the
> following comparison...
>
> Cos[45 Degree]
>
> Sin[45 Degree]
>
> Cos[x+y]//TrigExpand
> %/.y->45 Degree
>
> Cos[x+y]/.y->45 Degree
> %//TrigExpand
>
> In the first three examples, Mathematica recognizes that Cos[45 Degree] and Sin[45
> Degree] both have the exact value 1/Sqrt[2].
>
> In the fourth example it appears that Mathematica recognizes that (45 Degree) is
> ('an integer' Times 'something') and then tries to be (too) clever about
> expanding that before replacing the 'something' with Degree. This is further
> illustrated in the following example...
>
> Cos[x+45 z]
> %//TrigExpand
>
> So it's not that I thought the result was incorrect, I just thought that it
> is frustratingly complex for something that can be written so simply and
> which Mathematica will, in fact, obtain if you tickle it in just the right way.
>
> ~ BS ~
>
>
>
>



-- 
DrBob at bigfoot.com


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