Folium

Cartesian equation: (x^2+y^2)(y^2+x(x+b)) = 4axy^2

Polar equation: r = -b costheta + 4a costheta sin^2theta

Click below to see one of the Associated curves.

Definitions of the Associated curves

Evolute       Involute 1       Involute 2

 Inverse curve wrt origin      Inverse wrt another circle

Pedal curve wrt origin      Pedal wrt another point

Negative pedal curve wrt origin      Negative pedal wrt another point

   Caustic wrt horizontal rays      Caustic curve wrt another point

The general form of the folium is given by the formula above. The word 'folium' means 'leaf-shaped'.

There are three special forms of the folium, the simple folium, the double folium and the trifolium. These correspond to the cases

b = 4a, b = 0, b = a

respectively in the formula above.

The graph plotted above is the simple folium. There are separate entries for the double folium and the trifolium.

The simple folium is the pedal curve of the tricuspoid where the pedal point is one of the cusps.


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JOC/EFR February 1996