Folium of Descartes

Cartesian equation: x^3+y^3 = 3axy or x = 3at/(1+t^3), y = 3at^2/(1+t^3)

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

This folium was first discussed by Descartes in 1638 but, although he found the correct shape of the curve in the positive quadrant, he believed that this leaf shape was repeated in each quadrant like the four petals of a flower.

The problem to determine the tangent to the curve was proposed to Roberval who also wrongly believed the curve had the form of a jasmine flower. His name of fleur de jasmin was later changed.

The curve is sometimes known as the noeud de ruban.

The folium has an asymptote x+y+a = 0.

The equation of the tangent at the point with t = p is

p(p^3 - 2)x + (1 - 2p^3)y + 3ap^2 = 0.

The curve passes through the origin at t = 0 and approaches the origin a second time as t goes to infinity.


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JOC/EFR February 1996