We have 2 functions
f_{1}(x,y,z)=A_{1}xyz+B_{1}xy+C_{1}xz+D_{1}yz+E_{1  }x+G_{1}y+<br />
M_{1}z+N_{1}
f_{2}(x,y,z)=A_{2}xyz+B_{2}xy+C_{2}xz+D_{2}yz+E_{2  }x+G_{2}y+<br />
M_{2}z+N_{2}
So i need to find where f_{1}*f_{2}<0
Any ideas or mb u know where i can find solution?