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>