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MathGroup Archive 2005

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Re: a simplification problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55234] Re: [mg55172] a simplification problem
  • From: DrBob <drbob at bigfoot.com>
  • Date: Thu, 17 Mar 2005 03:29:20 -0500 (EST)
  • References: <200503161035.FAA23728@smc.vnet.net>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

That's not a simplification; it's the wrong answer. Here's the right one (based on the commonly used "branch" of the exponential):

ComplexExpand[(-1)^(1/3)]

1/2 + (I*Sqrt[3])/2

If you mean, "How do I extract the real third root of -1?", here's a method:

ComplexExpand[x /. Solve[x^3 == -1]]

{-1, 1/2 + (I*Sqrt[3])/2, 1/2 - (I*Sqrt[3])/2}

First@Select[%, FreeQ[#1, Complex] & ]

-1

Bobby

On Wed, 16 Mar 2005 05:35:49 -0500 (EST), Hui Fang <fangh73 at xmu.edu.cn> wrote:

> Dear All,
>
> My questions is simple:
> How do I simplify (-1)^(1/3) to -1?
>
> Thanks!
>
>
>
>



-- 
DrBob at bigfoot.com


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