ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY
Fermat's tangent method. Diagram and text from 'Varia Opera Mathematica' by the French mathematician Pierre de Fermat (1601-1665), showing his method for for finding the tangent of a curve. This method involves finding the subtangent for the point, which is described as the segment on the x-axis (vertical line) between the foot of the ordinate drawn to the point of contact (C) and the intersection of the tangent line with the x-axis (E). This page is from the 1679 edition.
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