# de L'Hôpital, Guillaume François Antoine, Marquis (1661–1704)

Guillaume de L'Hôpital was a French mathematician who wrote the first textbook on differential calculus, *Analyse des infiniment petits pour l'intelligence des lignes courbes* (1696). This contains the rule, now known as **L'Hôpital's Rule**,
for finding the limit of a rational function whose numerator and denominator
tend to zero at a point. Along with Isaac Newton,
Gottfried Leibniz, and Jacob Bernoulli,
de L'Hôpital was among the first to solve the brachistochrone
problem.