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Finding the real part of a symbolic complex expression

• To: mathgroup at smc.vnet.net
• Subject: [mg126580] Finding the real part of a symbolic complex expression
• From: Jacare Omoplata <walkeystalkey at gmail.com>
• Date: Sun, 20 May 2012 02:35:52 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com

I wanted to find the real part of (a + I b)(c + I d) , assuming a,b,c and d are real, "I" being Sqrt[-1].

So I tried,

Re[(a + I b) (c + I d)] /. Assuming -> Element[{a, b, c, d}, Reals]

Nothing happens. What I get for output is,

Re[(a+I b) (c+I d)]

I found out that I can use the function "ComplexExpand" to expand the expression assuming a,b,c and d to be real. But I'm curious to know if there a way to make Mathematica use "Re" to find the real part?

• Follow-Ups:
  • Re: Finding the real part of a symbolic complex expression
    • From: Murray Eisenberg <murray@math.umass.edu>
  • Re: Finding the real part of a symbolic complex expression
    • From: Bob Hanlon <hanlonr357@gmail.com>