Guillaume De l'Hôpital 
1661, Paris - 1704, Paris
Guillaume De l'Hôpital (auch: de l'Hospital) wrote the first textbook on calculus
in 1696 which was much influenced by the lectures of his teacher Johann Bernoulli, Jacob
Bernoulli and Leibniz.
L'Hôpital served as a cavalry officer but resigned because of
nearsightedness. From that time on he directed his attention to mathematics. L'Hôpital
was taught calculus by Johann Bernoulli in 1691.
L'Hôpital was a very competent mathematician and solved the
brachystochrone problem. The fact that this problem was solved independently by Newton, Leibniz and Jacob Bernoulli
puts l'Hôpital in very good company.
L'Hôpital's fame is based on his book Analyse des infiniment
petits pour l'intelligence des lignes courbes (1692) which was the first text-book to
be written on the differential calculus. In the introduction L'Hôpital acknowledges his
indebtedness to Leibniz, Jacob Bernoulli and Johann Bernoulli but L'Hôpital regarded the
foundations provided by him as his own ideas.
In this book is found 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:
Regel von de l'Hospital:
, falls f(x0) = g(x0) = 0
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