Manipulate[
PolarPlot[Cos[3θ],{θ,θmin,θmax},ImageSize->600,PlotRange->{{-1,1},{-1,1}}],
{{θmin,0},-π,0},{{θmax,0.001},0.001,π}]

Manipulate[Show[
ContourPlot3D[z==x^2+y^2,{x,-2,2},{y,-2,2},{z,-1,4},Mesh->None,ContourStyle->{Opacity[p],Orange},ImageSize->600],
ContourPlot3D[2*y==x^2+y^2,{x,-2,2},{y,-2,2},{z,-1,4},Mesh->None,ContourStyle->{Opacity[c]}],
ContourPlot3D[z==0,{x,-2,2},{y,-2,2},{z,-1,4},Mesh->None]
],
{{p,1,"Paraboloid Opacity"},0,1},{{c,1,"Cylinder Opacity"},0,1}]

Manipulate[Show[
ContourPlot3D[x==0,{x,-1,5},{y,-1,5},{z,0,5},Mesh->False,PlotRange->{{-0.5,5.5},{-0.5,5.5},{-0.5,5.5}},ImageSize->600,AxesOrigin->{0,0,0},ContourStyle->Opacity[0.9]],
ContourPlot3D[y==0,{x,-1,5},{y,-1,5},{z,0,5},Mesh->False,ContourStyle->Opacity[0.9]],
ContourPlot3D[z==2,{x,-1,5},{y,-1,5},{z,0,5},Mesh->False,ContourStyle->Opacity[0.9]],
ContourPlot3D[x+y+z==4,{x,-1,5},{y,-1,5},{z,0,5},Mesh->False,ContourStyle->Opacity[0.7]],
ParametricPlot3D[{t,2-t,2},{t,0,2},PlotStyle->{Thickness[0.008],Red,Opacity[B]}],
ParametricPlot3D[{0,0,t+2},{t,0,2},PlotStyle->{Thickness[0.008],Red,Opacity[B]}],
ParametricPlot3D[{0,t,2},{t,0,2},PlotStyle->{Thickness[0.008],Red,Opacity[B]}],
ParametricPlot3D[{t,0,2},{t,0,2},PlotStyle->{Thickness[0.008],Red,Opacity[B]}],
ParametricPlot3D[{0,t,4-t},{t,0,2},PlotStyle->{Thickness[0.008],Red,Opacity[B]}],
ParametricPlot3D[{t,0,4-t},{t,0,2},PlotStyle->{Thickness[0.008],Red,Opacity[B]}]
],{{B,0,"Show Edges of Solid"},{0,1}}]

Show[
ContourPlot3D[y==0,{x,-1.5,1.5},{y,-0.5,4.5},{z,-0.5,2.5},Mesh->False,PlotRange->{{-1.5,1.5},{-0.5,4.5},{-0.5,2.5}},ImageSize->600,AxesOrigin->{0,0,0},ContourStyle->Opacity[0.6]],
ContourPlot3D[y==4,{x,-1.5,1.5},{y,-0.5,4.5},{z,-0.5,2.5},Mesh->False,ImageSize->600,AxesOrigin->{0,0,0},ContourStyle->Opacity[0.6]],
ContourPlot3D[z==x^2,{x,-1.5,1.5},{y,-0.5,4.5},{z,-0.5,2.5},Mesh->False,ImageSize->600,AxesOrigin->{0,0,0},ContourStyle->Opacity[0.9]],
ContourPlot3D[z==2-x^2,{x,-1.5,1.5},{y,-0.5,4.5},{z,-0.5,2.5},Mesh->False,ImageSize->600,AxesOrigin->{0,0,0},ContourStyle->Opacity[0.9]]
]

Show[
ContourPlot3D[z==x^2+y^2,{x,-2.5,2.5},{y,-2.5,2.5},{z,0,4.5},Mesh->False,ContourStyle->Opacity[0.7],AxesOrigin->{0,0,0},ImageSize->600],
ContourPlot3D[z==4,{x,-2.5,2.5},{y,-2.5,2.5},{z,0,4.5},Mesh->False,ContourStyle->Opacity[0.7]]
]