Karl Friedrich Andreas Jacobi

Karl Friedrich Andreas Jacobi , also Carl Friedrich Andreas Jacobi , (born December 2, 1795 in Crawinkel , † June 28, 1855 in Schulpforta ) was a German mathematician and teacher.

Live and act

Jacobian figure with triangles ADB, BEC and CFA, angles of the same color are the same size

During his studies in Jena he became a member of the original fraternity . In 1817 he was a participant in the Wartburg Festival . From 1818 to 1819 he was vice rector in Brandenburg an der Havel and then until the end of his life professor of mathematics and physics at the grammar school in Schulpforta .

His younger brother Andreas Jacobi (1801-1875) also worked as a mathematician in Schulpforta.

Jacobi dealt with triangular geometry. The Jacobian figure is a triangle ABC with attachment triangles on the sides ( ), in which the neighboring angles in adjoining attachment triangles are the same. Jacobi proved that the transversals between the respective and the opposite corners of the triangle of origin ABC intersect at a point. This statement is known today as Jacobi's theorem. At Berkhan / Meyer and Florian Cajori he is counted with Karl Wilhelm Feuerbach , August Leopold Crelle and others among the mathematicians at the beginning of the 19th century in Germany who promoted triangular geometry, but whose work was carried out in the second half of the 19th century fell into oblivion. ${\ displaystyle ADB, BEC, CFA}$ ${\ displaystyle D_ {i}}$

In his work of 1825 he also gave a construction of the Brocard points of a triangle introduced by Crelle (rediscovered in 1875 by Henri Brocard ). They are defined as points inside the triangle, the lines connecting with the corners of the triangle form equal angles with the sides of the triangle.

In 1834 he published the Grondbeginsels der Meetkunde ( basics of geometry ) by Jean Henri van Swinden , published in Amsterdam in 1790 and 1816, with his own additions in German.

Fonts

De triangulorum rectilineorum proprietatibus quibusdam nondum satis cognitis , EB Schwickertum (Schwickert), Lipsiae (Leipzig) 1825 (Latin; program Gymnasium Pforta)
as editor: JH van Swinden's elements of geometry , Friedrich Frommann, Jena 1834 (original title Grondbeginsels der Meetkunde , 1816; translated from Dutch by Jacobi and provided with extensive additions)
De quadrangulorum proprietatibus quibusdam minus adhuc cognitis , Frommann, Jenae 1838 (Latin)
De proprietate rectarum punctum quoddam intra circulum ita transeuntium ut anguli, ad quos binae sibi proximae secantur, sint inter se aequales , Frommann, Jenae 1840 (Latin)
The points of removal of straight triangles. A geometric treatise , Friedr. Frommann, Jena 1851
- also The points of distance of straight triangles. A geometric treatise , Heinrich Sieling, Naumburg 1851 (with annual report of the Pforta State School)
The points of removal of straight triangles. II. The outer distant places. A geometric treatise , Friedr. Frommann, Jena 1854
- also the outer points of distance of straight triangles. A geometrical treatise , Heinrich Sieling, Naumburg 1854 (with annual report of the Pforta State School)

literature

Peter Kaupp (edit.): Stamm-Buch of the Jenaische Burschenschaft. The members of the original fraternity 1815-1819 (= treatises on student and higher education. Vol. 14). SH-Verlag, Cologne 2005, ISBN 3-89498-156-3 , p. 53.
Moritz Cantor : Jacobi, Karl Friedrich Andreas . In: Allgemeine Deutsche Biographie (ADB). Volume 13, Duncker & Humblot, Leipzig 1881, p. 593.
- in addition JC Poggendorff : Biographical-literary concise dictionary. First volume. A – L , Johann Ambrosius Barth, Leipzig 1856–1863, Sp. 1177 and Sp. 1576

Individual evidence

^ G. Berkhan , W. Fr. Meyer : Neuer Dreiecksgeometrie , Enzyklopädie der Mathematischen Wissenschaften , III, AB 10, S. 1219. It can be found in Jacobi De triangulorum ... , 1825
↑ Hans Walser: 99 points of intersections , MAA 2006, p. 135
^ Encyclopedia of Mathematical Sciences, III, AB 10, p. 1179
↑ Florian Cajori : A history of mathematics , Macmillan 1919, Reprint American Mathematical Society 2000, p. 298
^ Henri Brocard (1845-1922) was a French army officer.

personal data
SURNAME	Jacobi, Karl Friedrich Andreas
ALTERNATIVE NAMES	Jacobi, Carl Friedrich Andreas
BRIEF DESCRIPTION	German mathematician and teacher
DATE OF BIRTH	December 2, 1795
PLACE OF BIRTH	Crawinkel near Gotha
DATE OF DEATH	June 28, 1855
Place of death	School gate

[1] G. Berkhan , W. Fr. Meyer : Neuer Dreiecksgeometrie , Enzyklopädie der Mathematischen Wissenschaften , III, AB 10, S. 1219. It can be found in Jacobi De triangulorum ... , 1825

[2] Hans Walser: 99 points of intersections , MAA 2006, p. 135

[3] Encyclopedia of Mathematical Sciences, III, AB 10, p. 1179

[4] Florian Cajori : A history of mathematics , Macmillan 1919, Reprint American Mathematical Society 2000, p. 298

[5] Henri Brocard (1845-1922) was a French army officer.