Definition:Tangent Line/Historical Note
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Historical Note to Tangent Line
The definition of the tangent to a curve as the limit of a sequence of secants was made by Pierre de Fermat.
It first appeared in his Introduction to Plane and Solid Loci, but the idea most probably dates from considerably earlier.
This definition anticipates the invention of differential calculus.
In fact, Isaac Newton, in a letter that was discovered as late as $1934$, specifically states that it was the work of Fermat which inspired his own ideas about calculus.
Sources
- 1937: Eric Temple Bell: Men of Mathematics ... (previous) ... (next): Chapter $\text{IV}$: The Prince of Amateurs
- 1992: George F. Simmons: Calculus Gems ... (previous) ... (next): Chapter $\text {A}.13$: Fermat ($\text {1601}$ – $\text {1665}$)