Re: Finding the real part of a symbolic complex expression

*To*: mathgroup at smc.vnet.net*Subject*: [mg126586] Re: Finding the real part of a symbolic complex expression*From*: Bob Hanlon <hanlonr357 at gmail.com>*Date*: Mon, 21 May 2012 05:57:55 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <201205200635.CAA04268@smc.vnet.net>

expr = (a + I b) (c + I d); Simplify[Re[expr] // ExpandAll, Element[{a, b, c, d}, Reals]] a c - b d Re[expr] // ComplexExpand a c - b d Bob Hanlon On Sun, May 20, 2012 at 2:35 AM, Jacare Omoplata <walkeystalkey at gmail.com> wrote: > 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? >

**References**:**Finding the real part of a symbolic complex expression***From:*Jacare Omoplata <walkeystalkey@gmail.com>