Joseph Louis Lagrange (1735 - 1813) was a French mathematician and physicist. Born on January 25, 1736 in Turin, Italy, and died on April 10, 1813 in Paris. His father was an officer in the French Army Cavalry. He made historic contributions in the three disciplines of mathematics, mechanics and astronomy, of which his achievements in mathematics were the most outstanding. At the age of 18, Lagrange wrote his first paper in Italian, using Newton's Binomial Theorem to deal with the high-order differential quotient of the product of two functions. He then wrote the paper in Latin and sent it to the Berlin Academy of Sciences at that time. Euler, a mathematician. At the age of 19 in 1755, in the process of discussing the mathematical problem "Isoperimetric Problem", he used Euler's ideas and results as the basis and used pure analytical methods to find the extreme values of variations. The first paper,"Research on Methods of Maxima and Minima," developed the variational method pioneered by Euler and laid the theoretical foundation for the variational method. The creation of the variational method made Lagrange famous in Turin, and made him a professor at the Royal Artillery School in Turin at the age of 19, becoming a first-class mathematician recognized in Europe at that time. In 1756, on the recommendation of Euler, Lagrange was appointed as a corresponding academician of the Prussian Academy of Sciences. In 1764, the French Academy of Sciences offered a reward for an essay asking for gravity to explain the lunar balance problem. His research won an award. Then he successfully used the theory of differential equations and approximate solutions to study a complex six-body problem proposed by the Academy of Sciences (the motion problem of Jupiter's four moons), and won another award for this in 1766. When Frederick the Great of Germany invited Lagrange in 1766, he said that in the court of "the greatest king in Europe" there should be "the greatest mathematician in Europe." So he was invited to Berlin and served as director of the Mathematics Department of the Prussian Academy of Sciences. He lived there for 20 years, beginning the heyday of his life of scientific research. During this period, he completed the book Analytical Mechanics, an important classic mechanical work after Newton. In 1791, Lagrange was elected a member of the Royal Society. On April 3, 1813, Napoleon awarded him the Grand Cross of the Empire, but by this time Lagrange was bedridden. On the morning of April 11, Lagrange passed away.