Euler, Leonhard (1707-83), Swiss mathematician, whose major work was done in the field of pure mathematics, a field that he helped to found. Euler was born in Basel and studied at the University of Basel under the Swiss mathematician Johann Bernoulli, obtaining his master's degree at the age of 16. In 1727, at the invitation of Catherine I, empress of Russia, Euler became a member of the faculty of the Academy of Sciences in Saint Petersburg. He …showed first 75 words of 258 total…

…showed last 75 words of 258 total…treated the series expansion of functions and formulated the rule that only convergent infinite series can properly be evaluated. He also discussed three-dimensional surfaces and proved that the conic sections are represented by the general equation of the second degree in two dimensions. Other works dealt with calculus, including the calculus of variations, number theory, imaginary numbers, and determinate and indeterminate algebra. Euler, although principally a mathematician, made contributions to astronomy, mechanics, optics, and acoustics.