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Re: a simplification problem

• To: mathgroup at smc.vnet.net
• Subject: [mg55224] Re: [mg55172] a simplification problem
• From: Murray Eisenberg <murray at math.umass.edu>
• Date: Thu, 17 Mar 2005 03:28:49 -0500 (EST)
• Organization: Mathematics & Statistics, Univ. of Mass./Amherst
• References: <200503161035.FAA23728@smc.vnet.net>
• Reply-to: murray at math.umass.edu
• Sender: owner-wri-mathgroup at wolfram.com

(This sort of question keeps popping up in mathgroup.)

One answer is:

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

but that does NOT give you -1; rather it gives the principal cube root 
of -1, namely, 1/2 + (Sqrt[3]/2)I.

So there is no good reason that (-1)^(1/3) should simplify to -1.

Remember: Mathematica does not know you intended to form just real 
numbers here, so it wants to interpret such things in complex terms.


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

-- 
Murray Eisenberg                     murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305

• References:
  • a simplification problem
    • From: Hui Fang <fangh73@xmu.edu.cn>