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MathGroup Archive 2006

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Re: Is -1^(2/5) really undefined in R?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg69097] Re: [mg69075] Is -1^(2/5) really undefined in R?
  • From: János <janos.lobb at yale.edu>
  • Date: Wed, 30 Aug 2006 06:32:45 -0400 (EDT)
  • References: <200608290847.EAA00784@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On Aug 29, 2006, at 4:47 AM, Ben wrote:

> Is -1^(2/5) really undefined in R?
>
> Mathematica seems to think so, I guess since it looks like a  
> negative square root, but
>
> -1^(2/5) = (-1^2)^(1/5) = 1^(1/5) = 1
>
> Is this correct mathematically?
>
> cheers,
>
> BC


On my machine:

In[1]:=
-1^(2/5)
Out[1]=
-1

In[6]:=
(-1)^(2/5)
Out[6]=
(-1)^(2/5)

I think your first equal sign is incorrect.  it should be -(1)^2^ 
(1/5), but hey, I was never good in mathematics :)


János


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