Re: cannot solve *trivial* equation
- To: mathgroup at smc.vnet.net
- Subject: [mg34393] Re: cannot solve *trivial* equation
- From: Erk Jensen <Erk.Jensen at cern.ch>
- Date: Sat, 18 May 2002 03:50:53 -0400 (EDT)
- Organization: CERN http://www.cern.ch
- References: <ac2n7c$3qr$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Marco Manfredini wrote:
> Hi,
>
> I just tried a friend's Mathematica 4.0.0.0:
>
> Solve[{A == S + Q, Q == 2*S}, A]
>
> => {A->3*S}
>
> Solve[{A == S + Q, Q == 2*S}, S]
>
> => {}
>
> Can somebody explain this to me? (ie. "bug","you stupid")
>
> Marco
I'm not sure, but I'd say it's of the "you stupid" type ;)
two equations, two solutions!
Try the following and you'll see clearer:
Solve[{a == s + q, q == 2 s}, {q, s}]
Solve[a == s + q, s]
Solve[q == 2 s, s]
(BTW: it's good practice to use capitals for variables)
Your first (solving for A) worked since the second eq. doesn't contain A.
Ciao
-erk-
--
Dr.-Ing. Erk JENSEN mailto:Erk.Jensen at cern.ch
CERN PS/RF L19510 http://cern.ch/Erk.Jensen
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