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MathGroup Archive 2005

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Re: TrigExpand - Odd behavior

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55441] Re: TrigExpand - Odd behavior
  • From: stagat at linkline.com
  • Date: Wed, 23 Mar 2005 05:34:52 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

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 ~ 


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