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MathGroup Archive 1999

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Re: Real roots and other assumptions...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19928] Re: [mg19883] Real roots and other assumptions...
  • From: BobHanlon at aol.com
  • Date: Tue, 21 Sep 1999 02:22:56 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Janus,

In versions 3 or 4

Select[Solve[(x - 1)(x^2 + 1) == 0, x], FreeQ[x /. #, Complex] &]

{{x -> 1}}

Select[Solve[(x - 1)(x^2 + 1) == 0, x], Im[x /. #] == 0 &]

{{x -> 1}}

In version 4 only

Select[Solve[(x - 1)(x^2 + 1) == 0, x], Element[(x /. #), Reals] &]

{{x -> 1}}

Bob Hanlon

In a message dated 9/19/1999 9:59:06 PM, jaw at imf.au.dk writes:

>I keep encountering problems of the following type when using mathematica:
>I want to solve some equation(s) under some assumptions about the unknown(s),
>e.g. find the real roots of (x-1)(x^2+1).
>I've tried Solve[{Im[x]==0,(x-1)(x^2+1)==0},x]] for the above problem,
>but that
>doesn't get me anywhere.
>
>Is there a general way to let Mathematica know about such additional bounds
>as
>non-complexness etc? -- if so I would be happy to know it!
>


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