Re: Imposing constraints on a system of equations

*To*: mathgroup at smc.vnet.net*Subject*: [mg109367] Re: Imposing constraints on a system of equations*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Fri, 23 Apr 2010 03:50:28 -0400 (EDT)

Just use Reduce instead of Solve: sols = Reduce[eq1 && eq2 && eq3 && r >= 0 && h >= 0, {r, h, x}, Reals, Backsubstitution -> True] (a == 0 && r == 0 && h == 0) || (a == 0 && r == 0 && h > 0 && x == 0) || (a > 0 && r == Sqrt[a]/Sqrt[6*Pi] && h == Sqrt[2/(3*Pi)]*Sqrt[a] && x == -(Sqrt[a]/(2*Sqrt[6*Pi]))) On 22 Apr 2010, at 16:31, Virgil Stokes wrote: > A very simple question on imposing conditions/constraints. > > I know that a, r, and h must be real and non-negative in the following > system of equations: > > eq1=Pi*r^2+2*Pi*r*x==0; > eq2=2*Pi*r*h+(2*Pi*h+4*Pi*r)*x==0; > eq3=2*Pi*r^2+2*Pi*r*h-a==0; > sols=Solve[{eq1,eq2,eq3},{r,h,x}] > > How can I impose conditions on this system such that only real solutions > are obtained, and r and h are non-negative? > > Thank you, > --V > >