Scipione Dal Farro (14651526)

 Born in Italy.
 He developed the solution to the depressed cubic equation, but another mathematician received credit for it.
 Jean Gaston Darboux (18421917)
 Born in France.
 He contributed to differential geometry and to the theory of surfaces.
 Julius Wilhelm Richard Dedekind (18311916)
 Born in Germany.
 He produced an arithmetic definition of continuity and an exact formulation of the concept of the irrational number.
 He devised axioms that formally and exactly represented the logical concept of whole numbers.
 He introduced the concept of dual groups.
 Abraham Demoivre (16671754)
 Born in France.
 Working with Johann Heinrich Lambert, the two created that part of trigonometry which deals with imaginary quantities.
 Gérard Desargues (15911661)
 Born in France.
 He developed a form of geometry, now known as projective geometry.
 René Descartes (15961650)
 Born in France.
 In his history of philosophy, Discours de la Méthode, he placed an appendix, titled La Géométrie, which was the first published account of what is known today as analytic geometry.
 Diocles (ca. 240 – ca. 180 BCE)
 Born in Greece.
 He solved the problem of doubling the cube, with which Greek mathematicians had struggled for centuries.
 He solved the problem of cutting a sphere with a plane so that the volumes of the two sections are in a particular ratio to each other.
 Diophantus (fl. 270280 CE)
 Born in Alexandria.
 He devised the algebraic variable, in which a symbol stands for an unknown quantity.
 Equations needing only one symbol are now known as Diophantine equations.
 Lejeune Dirichlet (18051859)
 Born in Germany.
 He did research with the establishment of Fourier’s theorem.
 He researched the theory of numbers on asymptotiac laws.