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MathGroup Archive 2004

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RE: Complex Numbers

  • To: mathgroup at
  • Subject: [mg47439] RE: [mg47425] Complex Numbers
  • From: "David Park" <djmp at>
  • Date: Mon, 12 Apr 2004 03:44:53 -0400 (EDT)
  • Sender: owner-wri-mathgroup at


Give ComplexExpand a chance to work on the entire expression.

Re[Exp[a I] Exp[b I]] // ComplexExpand
Cos[a + b]

David Park
djmp at

From: Alejandro Vizcarra [mailto:gebankos at]
To: mathgroup at


I always have problems when dealing with complex numbers.  How can i
work with Mathematica in such a way that every expression will
be considered real unless it is declared explicitly complex (like a = 3 + 4
I ) ?

For example if I type

Re[ComplexExpand[ Exp[a I] Exp[b I]]]

I get the answer

-Im[Sin[ a+b]]+Re[Cos[a+b]]

Instead of simply Cos[a+  b]


Alejandro Vizcarra

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