Re: Question about Reduce
- To: mathgroup at smc.vnet.net
- Subject: [mg63914] Re: Question about Reduce
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Sun, 22 Jan 2006 00:52:28 -0500 (EST)
- Organization: The Open University, Milton Keynes, UK
- References: <dqsosn$c5k$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Mark Fisher wrote:
> The following behavior of Reduce puzzles me.
>
> conds = (5*Abs[67/30 - Sqrt[4489/900 - (18*(1 + x/3))/5]])/9 > 1 &&
> (5*Abs[67/30 + Sqrt[4489/900 - (18*(1 + x/3))/5]])/9 > 1;
>
> conds /. x -> 2
>
> returns True
>
> but
>
> Reduce[conds && x â?? Reals, {x}, Complexes] /. x -> 2
>
> returns False.
>
> Is that a bug or do I just not understand what Reduce should do?
>
> --Mark
>
Hi Mark,
*Reduce* is not able to solve the given inequalities (see In/Out[2]). A
possible approach is demonstrated in In[3]:
In[1]:=
conds =
(5*Abs[67/30 - Sqrt[4489/900 - (18*(1 + x/3))/5]])/
9 > 1 &&
(5*Abs[67/30 + Sqrt[4489/900 - (18*(1 + x/3))/5]])/
9 > 1
Out[1]=
5 67 4489 18 x
- Abs[-- - Sqrt[---- - -- (1 + -)]] > 1 &&
9 30 900 5 3
5 67 4489 18 x
- Abs[-- + Sqrt[---- - -- (1 + -)]] > 1
9 30 900 5 3
In[2]:=
Reduce[conds, x] /. x -> 2
Reduce::nsmet: This system cannot be solved with the methods available
to Reduce.
Reduce::ivar: 2 is not a valid variable.
Out[2]=
Reduce[True, 2]
In[3]:=
Reduce[conds && x == 2, x]
Out[3]=
x == 2
Best regards,
/J.M.