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MathGroup Archive 2005

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Re: TrigExpand - Odd behavior

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55423] Re: TrigExpand - Odd behavior
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Wed, 23 Mar 2005 05:34:35 -0500 (EST)
  • Reply-to: hanlonr at cox.net
  • Sender: owner-wri-mathgroup at wolfram.com

The unusual result that you obtain simplifies back to the original expression 
so it appears to be a legitimate representation.  This represenation is 
probably due to Degree being in symbolic form.  Use FunctionExpand to 
convert Degree to an exact numeric or manually convert Degree

expr=Cos[x+45 Degree];

expr//FunctionExpand//TrigExpand//Factor

(Cos[x] - Sin[x])/Sqrt[2]

(expr/.Degree->Pi/180)//TrigExpand//Factor

(Cos[x] - Sin[x])/Sqrt[2]

%==expr // FullSimplify

True


Bob Hanlon

> 
> From: "Bob Stagat" <stagat at linkline.com>
To: mathgroup at smc.vnet.net
> Date: 2005/03/22 Tue AM 03:51:07 EST
> To: mathgroup at smc.vnet.net
> Subject: [mg55423]  TrigExpand - Odd behavior
> 
> 
> 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 ~
> 
> 


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