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MathGroup Archive 2006

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Re: Why is the negative root?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg69503] Re: [mg69474] Why is the negative root?
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Thu, 14 Sep 2006 06:56:11 -0400 (EDT)
  • Reply-to: hanlonr at cox.net

Looks like a bug. Make the substition first

Clear[z];

z/.(Reduce[{z^3-z^2- b z-1==0/.b->3, z>0}, z]//ToRules)

1 + Sqrt[2]


Bob Hanlon

---- p-valko at tamu.edu wrote: 
> (Reduce[{z^3-z^2- b z-1==0, b>0, z>0}, z] //ToRadicals)/.b->3.//Chop
> 
> gives a negativ z:
> 
> z == - 0.414214
> 
> What am I doing wrong?
>  
> Regards
> Peter
> 

--

Bob Hanlon
hanlonr at cox.net



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