# Leonhard Euler

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Leonhard Euler (/ˈɔɪlər/ OY-lər,[lower-alpha 1] German: [ˈɔʏlɐ] ();[lower-alpha 2] 15 April 1707  18 September 1783) was a Swiss mathematician, physicist, astronomer, geographer, logician and engineer who founded the studies of graph theory and topology and made pioneering and influential discoveries in many other branches of mathematics such as analytic number theory, complex analysis, and infinitesimal calculus. He introduced much of modern mathematical terminology and notation, including the notion of a mathematical function.[6] He is also known for his work in mechanics, fluid dynamics, optics, astronomy and music theory.

Quick facts: Leonhard Euler, Born, Died, Alma mater, ...
Leonhard Euler
Portrait by Jakob Emanuel Handmann (1753)
Born15 April 1707
Died18 September 1783 (aged 76)
[OS: 7 September 1783]
Alma materUniversity of Basel (MPhil)
Known for
Spouse
Katharina Gsell
(m. 1734; died 1773)
Salome Abigail Gsell
(m. 1776)
Scientific career
FieldsMathematics and physics
Institutions
ThesisDissertatio physica de sono (Physical dissertation on sound) (1726)
Euler is credited for popularizing the Greek letter ${\displaystyle \pi }$ (lowercase pi) to denote the ratio of a circle's circumference to its diameter, as well as first using the notation ${\displaystyle f(x)}$ for the value of a function, the letter ${\displaystyle i}$ to express the imaginary unit ${\displaystyle {\sqrt {-1}}}$, the Greek letter ${\displaystyle \Sigma }$ (capital sigma) to express summations, the Greek letter ${\displaystyle \Delta }$ (uppercase delta) for finite differences, and lowercase letters to represent the sides of a triangle while representing the angles as capital letters.[12] He gave the current definition of the constant ${\displaystyle e}$, the base of the natural logarithm, now known as Euler's number.[13]