Conic Constructions Using Other Directrix

Using f(x) = sin(x) as a directrix.
Using f(x) = x[sup]3[/sup] / 16 as a directrix.
Using f(x) = floor(x) as a directrix.
Using an ellipse as a directrix.
– Steve Phelps

Information: Conic Constructions Using Other Directrix