# 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.

## Sources

- 1968: Murray R. Spiegel:
*Mathematical Handbook of Formulas and Tables*: $11.24$: Special Plane Curves - 1992: George F. Simmons:
*Calculus Gems*... (previous) ... (next): Chapter $\text {A}.13$: Fermat ($1601$ – $1665$) - 2008: Ian Stewart:
*Taming the Infinite*... (previous) ... (next): Chapter $6$: Curves and Coordinates