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Re: Cube root of -1 and 1

  • To: mathgroup at smc.vnet.net
  • Subject: [mg91032] Re: Cube root of -1 and 1
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Mon, 4 Aug 2008 03:23:08 -0400 (EDT)
  • References: <g6h5fm$h26$1@smc.vnet.net>

Hi,

because (-1)^(1/3)
is not -1, it is
1/2 + (I/2)*Sqrt[3]

Regards
   Jens

Bob F wrote:
> Could someone explain why Mathematica evaluates these so differently?
> 
> In[53]:=
> 
> (Sqrt[36] - 7)^(1/3)
> (Sqrt[36] - 5)^(1/3)
> 
> Out[53]= (-1)^(1/3)
> 
> Out[54]= 1
> 
> In other words why isn't (-1)^1/3 expressed as -1 ??
> 
> Thanks...
> 
> -Bob
> 


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