Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2008

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Does Mathematica think Sqrt[2] is rational?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg86678] Re: Does Mathematica think Sqrt[2] is rational?
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Tue, 18 Mar 2008 04:49:20 -0500 (EST)

On 3/17/08 at 12:22 AM, maderri2 at gmail.com (magma) wrote:

>expr2 = Exists[{x, y}, x^2 == 2 y^2]

>Mathematica correctly finds out that expr is true over the reals

>Reduce[expr2, {x, y}, Reals]

>But gives a wrong answer over the integers or the rationals

>Reduce[expr2, {x, y}, Integers]

>Reduce[expr2, {x, y}, Rationals]

I believe you are overlooking the trivial solution

In[5]:= Assuming[x \[Element] Integers && y \[Element] Integers,
 FindInstance[expr2, {x, y}]]

Out[5]= {{x->0,y->0}}


  • Prev by Date: Re: Does Mathematica think Sqrt[2] is rational?
  • Next by Date: Question on looping FindRoot
  • Previous by thread: Re: Does Mathematica think Sqrt[2] is rational?
  • Next by thread: Re: Does Mathematica think Sqrt[2] is rational?