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*x==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}]