Plot3D[{-2,(x^2)+(y^2)},{x,-2,2},{y,-2,2},PlotStyle->{Opacity[0.2]},MeshFunctions->(((#1)^2)+((#2)^2) &),RegionFunction->Function[{x,y,z},x^2+y^2≤4],BoxRatios->Automatic,PlotPoints->30]

ContourPlot[(x^2)+(y^2),{x,-2,2},{y,-2,2}]

ContourPlot[(x^2)+(y^2),{x,-2,2},{y,-2,2},ContourShading->False,ContourLabels->True]

ContourPlot[(x^2)+(y^2)==1,{x,-2,2},{y,-2,2}]

ContourPlot3D[{z== -2,z== (x^2)+(y^2)},{x,-2,2},{y,-2,2},{z,-2.2,4},ContourStyle->{Opacity[0.2]},MeshFunctions->(((#1)^2)+((#2)^2) &)]

ParametricPlot3D[{{r Cos[θ],r Sin[θ],-2},{r Cos[θ],r Sin[θ],(r^2)}},{θ,0,2π},{r,0,2},PlotStyle->{Opacity[0.2]}]

ContourPlot[(3/4) y^2+(1/24) y^3-(1/32)y^4-x^2,{x,-7,7},{y,-7,7},ContourShading->False,ContourLabels->True,Contours->Table[-10+k,{k,1,16}]]

Table[(k^2),{k,1,20}]

Plot3D[(3/4) y^2+(1/24) y^3-(1/32)y^4-x^2,{x,-7,7},{y,-7,7},RegionFunction->Function[{x,y,z},(3/4) y^2+(1/24) y^3-(1/32)y^4-x^2≥ -8],MeshFunctions->(#3 &),MeshStyle->{Blue,Thick}]

a=Plot3D[{0,1 + x y},{x,0,2},{y,0,1},Mesh->False,PlotStyle->{Opacity[0.2]}]

b=ParametricPlot3D[{1,y,t(1+y)},{y,0,1},{t,0,1},Mesh->False,BoundaryStyle->Thick,PlotStyle->{Opacity[0.2],Blue}]

Show[a,b]