what are some of the famous works of that third mathematician mentioned in the list?
He made significant contributions to the fields of analysis, number theory, and both classical and celestial mechanics, such as  analytical mechanics ("Mécanique analytique", 4. ed., 2 vols. Paris: Gauthier-Villars et fils, 1788–89)
Joseph-Louis Lagrange
He made significant contributions to the fields of analysis, number theory, and both classical and celestial mechanics.

In 1766, on the recommendation of Swiss Leonhard Euler and French d'Alembert, Lagrange succeeded Euler as the director of mathematics at the Prussian Academy of Sciences in Berlin, Prussia, where he stayed for over twenty years, producing volumes of work and winning several prizes of the French Academy of Sciences. 
when do we considered a group to be a set In mathematics, a group is a set equipped with a binary operation that combines any two elements to form a third element in such a way that four conditions called group axioms are satisfied, namely closure, associativity, identity and invertibility. what are some of the examples considered to be a set? One of the most familiar groups is the set of integers formula_1 which consists of the numbers. name some famous mathematicians who were involved in the development of these sets. Évariste Galois, Paolo Ruffini, Joseph-Louis Lagrange. what was the famous theory the first mathematician developed? Galois' most significant contribution to mathematics is his development of Galois theory. what does this theory state? It sates that an equation could be solved in radicals if one can find a series of subgroups of its Galois group, each one normal in its successor with abelian quotient, or its Galois group is solvable. what is this mathematician's date of birth? 25 October 1811. which educational institutions did he attend? Lycée Louis-le-Grand where is this education institution located? Paris apart from the discussed mathematical theory he developed, what were his other contributions in the mathematical field? Within the 60 or so pages of Galois' collected works are many important ideas that have had far-reaching consequences for nearly all branches of mathematics. what were some of the famous works of that second mathematician mentioned in the list? Among his work was an incomplete proof (Abel–Ruffini theorem) that quintic (and higher-order) equations cannot be solved by radicals, and Ruffini's rule which is a quick method for polynomial division.
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Joseph-Louis Lagrange [SEP] Introduction
Lagrange's treatise on analytical mechanics ("Mécanique analytique", 4. ed., 2 vols. Paris: Gauthier-Villars et fils, 1788–89), written in Berlin and first published in 1788, offered the most comprehensive treatment of classical mechanics since Newton and formed a basis for the development of mathematical physics in the nineteenth century. In 1787, at age 51, he moved from Berlin to Paris and became a member of the French Academy of Sciences. He remained in France until the end of his life. He was instrumental in the decimalisation in Revolutionary France, became the first professor of analysis at the École Polytechnique upon its opening in 1794, was a founding member of the Bureau des Longitudes, and became Senator in 1799.