David's most important contribution is the development of algebra. He systematically introduced algebraic symbols for the first time and promoted the development of equation theory. David used the word "analysis" to summarize the contents and methods of algebra at that time. He created a large number of algebraic symbols, replaced unknowns with letters, systematically expounded and perfected the solution of cubic equation, pointed out the relationship between roots and coefficients, and gave a triangular solution to the irreducibility of cubic equation. His main work is Introduction to Analysis.

Descartes 1596- 1650

French mathematician, scientist and philosopher. He is one of the founders of modern western bourgeois philosophy. His philosophy and mathematical thoughts have had a far-reaching impact on history. People carved a sentence on his tombstone: "Descartes, the first person who fought for and guaranteed rational rights for mankind since the European Renaissance."

Cardang (1501-1576)

In the book "Important Art" published in 1545, the general solution of cubic equation was published, which was called "Cardan formula" by later generations. He was the first mathematician to write the square root of a negative number into a formula. When discussing whether it was possible to divide 10 into two parts so that their product was equal to 40, he wrote the answer as =40, although he thought it was equal to these two. But he still divided 10 into two parts and made their product equal to 40. The name "imaginary number" was given by Descartes (1596- 1650), who put forward "imaginary number" and "imaginary number" in Geometry (published by 1637).