Re: a fault in the Factor[] function for polynomials?

• To: mathgroup at smc.vnet.net
• Subject: [mg70414] Re: a fault in the Factor[] function for polynomials?
• From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
• Date: Mon, 16 Oct 2006 02:34:00 -0400 (EDT)
• Organization: The Open University, Milton Keynes, UK
• References: <egse02\$cpp\$1@smc.vnet.net>

Roger Bagula wrote:
> Expand[(x^4 + 2*Sqrt[3]x^2 - 1)(x^4 - 2*Sqrt[3]x^2 - 1)]
> 1 - 14x^4 + x^8
> Factor[%]
> (1 - 4x^2 + x^4)(1 + 4x^2 + x^4)
>
In[1]:=
expr1 = Expand[(x^4 + 2*Sqrt[3]*x^2 - 1)*
(x^4 - 2*Sqrt[3]*x^2 - 1)]

Out[1]=
4    8
1 - 14 x  + x

In[2]:=
expr2 = Factor[expr1]

Out[2]=
2    4          2    4
(1 - 4 x  + x ) (1 + 4 x  + x )

In[3]:=
Simplify[expr1 == expr2]

Out[3]=
True

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