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Re: TraditionForm Appears to be Inconsistent

  • To: mathgroup at
  • Subject: [mg99576] Re: [mg99551] TraditionForm Appears to be Inconsistent
  • From: Murray Eisenberg <murray at>
  • Date: Fri, 8 May 2009 00:16:53 -0400 (EDT)
  • Organization: Mathematics & Statistics, Univ. of Mass./Amherst
  • References: <>
  • Reply-to: murray at

Because, I presume, Mathematica knows that Cos[x] always has the same 
value as Sin[x + \[Pi]/2] no matter what x is; it evaluates both sides 
of that equation and then decrees the equation True.

But Mathematica seems cautious if, for example, you enter

   Cos[a + b I] + Sin[a + b I]

which it leaves unevaluated further.  Then if you enter, say,

   Exp[I \[Theta]]==Cos[\[Theta]]+I Sin[\[Theta]]/.\[Theta]->a+b I

then it returns the result without further evaluation. at wrote:
> Hi
> The Mathematica 7 documentation says that
> TraditionalForm[Exp[I \[Theta]] == Cos[\[Theta]] + I Sin[\[Theta]]]
> will display the expression in traditional form, and indeed it does.
> However, the following evaluates the expression and then displays True
> in traditional form:
> TraditionalForm[Cos[x] == Sin[x + \[Pi]/2]]
> Why is TraditionalForm behaving differently in these two apparently
> identical situations, and how can I get Mathematica to display this
> trigonometric identity in traditional form?
> Thanks in advance
> Chris

Murray Eisenberg                     murray at
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305

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