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Re: Error in solving inequalities

  • To: mathgroup at smc.vnet.net
  • Subject: [mg125186] Re: Error in solving inequalities
  • From: Szabolcs <szhorvat at gmail.com>
  • Date: Mon, 27 Feb 2012 06:40:12 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <jictn2$enl$1@smc.vnet.net>

On Sunday, 26 February 2012 11:23:46 UTC+2, Franco  wrote:
> Hi,
> I cannot understand why solving
> Reduce[(x^2/x )>= 0, x]
> I get the result x>=0.
> 
> Clearly the inequality has not meaning for x=0.
> 
> Thanks a lot for your anwers.
> 

If you type x^2/x >= 0, Mathematica automatically returns x >= 0.  This is the expression Reduce sees.  It's not difficult to see that there are so many advantages to this simplification being automatically done.

However Reduce is usually smart enough about these things.  If you pass it x^2 / (x-1) >= 0 (which does not auto-simplify, so Reduce can see the expression as you entered it), it will return x == 0 || x > 1.



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