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'''Leonhard Euler''' (''1707-1783'', pronounced ''Oiler'') was a famous Swiss [[mathematician]]. He made numerous contributions to many fields of [[mathematics]] and [[science]]. Euler is often considered to be one of the greatest mathematicians of all time, along with [[Isaac Newton]], [[Archimedes]], and [[Carl Friedrich Gauss]].<br />
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== Biography ==<br />
Euler was born on April 15, 1707 in Basel, Switzerland. Euler's parents were Paul Euler, a pastor of the Reformed Church, and Marguerite Brucker, a pastor's daughter. He had two young sisters, named Anna Maria and Maria Magdalena. At the age of thirteen he enrolled at the [[University of Basel]].<br />
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On January 7, 1734, he married Katharina Gsell. The young couple had thirteen children, only five of whom survived childhood.<br />
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After suffering a near-fatal fever in 1735, Euler became nearly blind in his right eye. Soon after his return to Russia in 1766, he became almost completely blind in his left eye. Despite his horrible eyesight, Euler continued his prolific research. <br />
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Even as an old man, Euler was famous for being able to calculate difficult arithmetic quickly in his head.<br />
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On September 18, 1783, Euler passed away in St. Petersburg, Russia after suffering a brain hemorrhage. He was buried in the Alexander Nevsky Monastery.<br />
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== Contributions to Mathematics ==<br />
* In 1735, Euler showed that <math>\zeta(2) = \frac{\pi^2}6</math> where <math>\zeta</math> is the [[zeta function]].<br />
* [[Euler's polyhedral formula]] states that for any [[convex]] [[polyhedron]], with <math>V</math>, <math>E</math> and <math>F</math> denoting the number of [[vertex|vertices]], [[edge]]s, and [[face]]s, respectively, <math>V-E+F=2</math>.<br />
* [[Euler's totient theorem]] is a theorem related to [[Euler's totient function]], or the sum of all numbers relatively prime to a number and less than it.<br />
* [[Euler's identity]] is a famous identity of [[complex numbers]] which states that <math>e^{i\theta}=\cos(\theta)+i\sin(\theta)</math> for all <math>\theta</math>.<br />
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=== Functions ===<br />
Euler was the first to use the notation <math>f(x)</math>, and also was the first to call such structures [[function]]s. This led to great advancements in [[calculus]] and [[algebra]].<br />
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=== Analysis ===<br />
Euler contributed greatly to the expansion of a branch of [[mathematics]] called [[analysis]]. His achievements often involved [[power series]]. He is also credited with discovering [[Euler's constant]], denoted as <math>e</math>. Euler discovered that <br />
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<cmath>e^x = \sum_{n=0}^\infty {x^n \over n!} = \lim_{n \to \infty}\left(\frac{1}{0!} + \frac{x}{1!} + \frac{x^2}{2!} + \cdots + \frac{x^n}{n!}\right)</cmath><br />
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He also discovered the power series for the [[tangent function|arctengent]], which is<br />
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<cmath>\lim_{n \to \infty}\left(\frac{1}{1^2} + \frac{1}{2^2} + \frac{1}{3^2} + \cdots + \frac{1}{n^2}\right) = \frac{\pi ^2}{6}</cmath><br />
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==Physics==<br />
Euler helped the wave theory of [[light]] become the dominant idea for most of the nineteenth century. He also made several other contributions to [[optics]], such as disagreeing with [[Isaac Newton]]'s theory of light. <br />
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In addition, he made several important discoveries in [[astronomy]] and [[mechanics]].<br />
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== See Also ==<br />
* [[Euler's line]]<br />
* [[Euler's identity]]<br />
* [[Euler's constant]]<br />
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==External Links==<br />
* [http://www-groups.dcs.st-and.ac.uk/~history/Biographies/Euler.html Biography of Euler]<br />
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[[Category:Famous mathematicians]]</div>33286