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MathGroup Archive 2007

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Re: Re: Factorizing...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg74145] Re: [mg74094] Re: Factorizing...
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Mon, 12 Mar 2007 22:08:40 -0500 (EST)

Note that Factor in the code below does not do anything at all, it is  
simply stripped. The point is, of course that the original post was  
not only syntacticaly incorrect but Mathematically nonsensical, since  
an algebraic number can be obviously factored in infinitley many ways  
so how could "Factor" choose one of them? One way to get what the  
poster wanted is simply:


RootReduce[(2 + Sqrt[5])^(1/3)]


(1/2)*(1 + Sqrt[5])


Andrzej Kozlowski


On 10 Mar 2007, at 12:46, Jean-Marc Gulliet wrote:

> Bruno Campanini wrote:
>> How can I get it from Mathematica:
>>
>> Factor[2+SQR(5)] = ((1+SQR(5))/2)^3
>
> Using the correct syntax strongly helps. See " The Mathematica Book
> Online  /  A Practical Introduction to Mathematica  /  Numerical
> Calculations  /  1.1.3 Some Mathematical Functions" at
> http://documents.wolfram.com/mathematica/book/section-1.1.3
>
> In[1]:=
> Simplify[Factor[2 + Sqrt[5]] == ((1 + Sqrt[5])/2)^3]
>
> [...disregard the warning message...]
>
> Out[1]=
> True
>
> Regards,
> Jean-Marc
>
> [1] "The Mathematica Book /  A Practical Introduction to  
> Mathematica  /
>   Numerical Calculations  /  1.1.3 Some Mathematical Functions",
> http://documents.wolfram.com/mathematica/book/section-1.1.3
>



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