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MathGroup Archive 1999

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Re: equaltity of lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19193] Re: equaltity of lists
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Tue, 10 Aug 1999 02:52:50 -0400
  • References: <7o5ih1$rml@smc.vnet.net> <7ofaab$pnq$9@dragonfly.wolfram.com>
  • Sender: owner-wri-mathgroup at wolfram.com

F. Mittermayr <mitterma at linz.vai.co.at> wrote in message
news:7ofaab$pnq$9 at dragonfly.wolfram.com...
> Why do I get the answer True when I ask Mathematica
>
> a=x; b=x^2/x;
> {a,b}=={b,a}
>
> Is it really true? What's about x=0?
>
> Regards
> F. Mittermayr
>

Because of

In[1]:=
x^2/x

Out[1]=
x

This is formal algebra that ignores special cases. It takes the generic
situation like
Solve with

In[2]:=
Solve[y x == 1, y]

Out[2]=
{{y -> 1/x}}

Whereas we get

In[3]:=
Reduce[y x == 1, y]

Out[3]=
y == 1/x && x != 0

Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565




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