ContourPlot Examples

ContourPlot[{x1^2+x1*x2+x2^2+2*x1+6*x2+3==0,
                           x1^2+x1*x2-x2^2+2*x1+6*x2+3==0,
                           x1^2-x1*x2+x2^2+2*x1+6*x2+3==0,
             -x1^2+x1*x2+x2^2+2*x1+6*x2+3==0},
                     {x1,-10,10},{x2,-10,10},ContourStyle->"Pastel",
            GridLines->Automatic,ImageSize->Large,
PlotLegends->"Expressions"]