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Strange Behaviour of Solve?

• To: mathgroup at smc.vnet.net
• Subject: [mg79007] Strange Behaviour of Solve?
• From: Andreas Maier <andimai at web.de>
• Date: Sun, 15 Jul 2007 01:13:30 -0400 (EDT)

Hi,

i tried (using Mathematica 6.0) to solve a system of equations:

In:=Solve[{b == g, a == (g*v/c), (b)^2 + (a)^2 == 1}, g]
Out:={}

But when i use

In:=Solve[{b == g, a == (g*v/c), (b)^2 + (a)^2 == 1}, {a, b, g}]
Out={{g -> -c/Sqrt[c^2 + v^2], b -> -c/Sqrt[c^2 + v^2],
          a -> -v/Sqrt[c^2 + v^2]}, {g -> c/Sqrt[c^2 + v^2],
          b -> c/Sqrt[c^2 + v^2], a -> v/Sqrt[c^2 + v^2]}}

i suddenly get the solution for g. It seems to me, that the number
of solutions for one variable depends on the number of variables
i want to solve for. Is this behaviour of Solve to be
expected?

Andreas Maier

• Follow-Ups:
  • Re: Strange Behaviour of Solve?
    • From: Andrzej Kozlowski <akoz@mimuw.edu.pl>