# Definition:Folium of Descartes

## Definition

The folium of Descartes is the locus of the equation:

$x^3 + y^3 - 3 a x y = 0$

## Source of Name

This entry was named for René Descartes.

## Historical Note

Marin Mersenne had communicated to René Descartes the method devised by Pierre de Fermat for calculating the tangent to a curve.

René Descartes seems to have thought little of this method, believing that it was not sufficiently general to be useful.

The curve now known as the folium of Descartes was used by him as a challenge to Fermat, believing that he would be unable to use this method on it.

Reportedly he was seriously annoyed at Fermat when the latter solved it without any trouble.