Re: Finding the real part of a symbolic complex expression

*To*: mathgroup at smc.vnet.net*Subject*: [mg126582] Re: Finding the real part of a symbolic complex expression*From*: "Nasser M. Abbasi" <nma at 12000.org>*Date*: Mon, 21 May 2012 05:56:32 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <jpa3ea$468$1@smc.vnet.net>*Reply-to*: nma at 12000.org

On 5/20/2012 1:36 AM, Jacare Omoplata 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? > -------------------- expr=(a+I b)(c+I d); ComplexExpand[Re[expr]] ---------------------- Out[12]= a c-b d ----------------------------- Assuming[{Element[{a,b,c,d},Reals]},Simplify[Re[Expand[expr]]]] ----------------------------- Out[15]= a c-b d --Nasser