Lagrange found Greek geometry dull until a stray paper hooked him at seventeen
As a law student in Turin, Giuseppe Lagrangia preferred Latin and found geometry boring. At seventeen he stumbled on a paper by Edmond Halley, taught himself mathematics in a year, and within a decade was trading ideas with Euler. He went on to rewrite mechanics without a single diagram and to help decimalise France.
Born in Turin on 25 January 1736, the eldest of eleven children, he came from a family of mixed Italian and French descent; his father, a treasury official, lost most of his fortune in speculation. By 1755 the young self-taught mathematician was assistant professor at Turin's royal artillery school, reportedly the first person to teach calculus in an engineering school. From 1754 he was writing to Euler about a new method for finding the maximum or minimum of whole functions, the germ of the calculus of variations. Euler, impressed, is said to have held back his own overlapping paper so the young man could finish. In 1757 Lagrange co-founded the society that became the Turin Academy of Sciences.
Euler and Maupertuis tried to lure him to Berlin as early as 1756, but he shyly declined, reportedly feeling Berlin was no place for him while Euler was there. When Euler left for Saint Petersburg in 1766, Frederick the Great wrote that the greatest king in Europe wished to have the greatest mathematician in Europe at his court. Lagrange stayed more than twenty years, and there wrote his Mécanique analytique of 1788, the most complete treatment of mechanics since Newton.
His results reach across mathematics: the Euler–Lagrange equations, the method of Lagrange multipliers for problems with constraints, variation of parameters for differential equations, a proof that any whole number can be built by adding four square numbers, and work anticipating group theory. He also explained why the Moon keeps one face toward Earth.
His wife Vittoria died in 1783 after long illness, leaving him depressed, and after Frederick's death he accepted Louis XVI's invitation to Paris in 1787. He survived the Terror, exempted by name, reportedly through Antoine Lavoisier's intervention; after Lavoisier's execution Lagrange lamented that a moment had cut off a head a century could not replace. He helped design the decimal system, took the Polytechnique's new chair of analysis when the school opened in 1794, and was made a senator in 1799. He died on 10 April 1813.
Source: Joseph-Louis Lagrange
