Re: Strange empty set of solutions

*To*: mathgroup at smc.vnet.net*Subject*: [mg71814] Re: Strange empty set of solutions*From*: José Carlos Santos <jcsantos at fc.up.pt>*Date*: Thu, 30 Nov 2006 06:05:04 -0500 (EST)*References*: <ekh7pg$sgs$1@smc.vnet.net> <ekjfrf$d7h$1@smc.vnet.net>

On 29-11-2006 8:19, Jens-Peer Kuska wrote: > and we can't read you mind and the memory of your computer > so we must imagine a matrix M and write down Do you want an example? Here it is: M = {{4/5(c - 1), -2/Sqrt[5]s, 2/5(1 - c)}, {2/5(1 - c), -1 + s/Sqrt[5], 4/5 + c/5}, {-2s/Sqrt[5], -c, -1 + s/Sqrt[5]}} // N with c = Cos[Sqrt[5]] and s = Sin[Sqrt[5]]. If I type Solve[{M.{x, y, z} == {0, 0, 0}}, {x, y, z}] I get {{x -> 0. - 0.0438861 z, y -> 0. + 1. z}} but if I type Solve[{M.{x, y, z} == {0, 0, 0}, x^2 + y^2 + z^2 == 1}, {x, y, z}] then I get the empty set. Why is that? Best regards, Jose Carlos Santos