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**Albert girard** was born in 1595 in St Mihiel (France) and died on December 8, 1632 in Leiden (Netherlands). He was French, but emigrated as a religious refugee to the Netherlands. He first attended the University of Leiden at the age of 22, where he studied mathematics. However, his first interest was music.

Worked in algebra, trigonometry and arithmetic. In 1626 he published a treatise on trigonometry containing the first abbreviations sen, cos, tag. It also provided formulas for calculating the triangle area. In algebra he developed sketches of the fundamental algebra theorem and translated Stevin's works in 1625.

It is also famous for being the first to formulate f_{n + 2} = f_{n + 1} + f_{no}, which is the definition of Fibonacci's succession.

Girard devoted much of his time to engineering in the Dutch Army, although it was probably after the publication of his work on trigonometry. In 1629, he wrote * Invention Nouvelle en l'algèbre* (1629), demonstrating that the equations could have negative and imaginary roots.

As a teacher, he taught mathematics, engineering, optics and music. Sponsored by the court, he also researched the law of refraction and devoted much of his time to engineering in the Dutch Army, especially fortification projects and cartography.