Others!!!

  Approach to tangent lines was applied in the 1640's by an Italian physicist and student of Galileo, Evagelista Torricelli (1608-1647), and by a French mathematician Gills Persone de Roberval (1602-1675). They used this approach to determine tangent lines to a variety of curves, including those given in modern notation by the equation  with various rational exponents n.

  In the 1960’s, an American mathematician, Abraham Robinson, devised a rigorous notion of infinitesimal. It involves an abstract mathematical structure that avoids consideration of the "infinitely small". Calculus based on Robinson's infinitesimals is known as nonstandard analysis.