Thomas Jacobsen Fincke was born in
Flensburg in
Schleswig. Fincke was the son of Councillor Jacob Fincke and Anna Thorsmede. He completed his primary schooling at Flensburg. From 1577, he studied mathematics, rhetoric and other philosophical studies for five years at the
University of Strasbourg. Fincke's lasting achievement is found in his book
Geometria rotundi (1583), in which he introduced the modern names of the
trigonometric functions
tangent and
secant. In 1590, he became professor of mathematics at the
University of Copenhagen. In 1603 he also obtained a professorship in medicine. ==Personal life==