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Re: Finding the real part of a symbolic complex expression


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?
>



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