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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: [mg69112] RE: [mg69075] Is -1^(2/5) really undefined in R?
  • From: "David Park" <djmp at earthlink.net>
  • Date: Wed, 30 Aug 2006 06:33:53 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Solve[-1^2 == z^5, z]
{{z -> -1}, {z -> (-1)^(1/5)}, {z -> -(-1)^(2/5)},
  {z -> (-1)^(3/5)}, {z -> -(-1)^(4/5)}}

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/


From: Ben [mailto:ben.carbery at spam.me]
To: mathgroup at smc.vnet.net


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



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