# determine the region where product <0

$f_{1}(x,y,z)=A_{1}xyz+B_{1}xy+C_{1}xz+D_{1}yz+E_{1 }x+G_{1}y+
$f_{2}(x,y,z)=A_{2}xyz+B_{2}xy+C_{2}xz+D_{2}yz+E_{2 }x+G_{2}y+
So i need to find where $f_{1}*f_{2}<0$