Karl Wilhelm Feuerbach (30 May 1800 – 12 March 1834) was a German

geometer A geometer is a mathematician whose area of study is geometry. Some notable geometers and their main fields of work, chronologically listed, are: 1000 BCE to 1 BCE * Baudhayana (fl. c. 800 BC) – Euclidean geometry, geometric algebra * ...

and the son of legal scholar

Paul Johann Anselm Ritter von Feuerbach Paul Johann Anselm Ritter von Feuerbach (14 November 177529 May 1833) was a German legal scholar. His major achievement was a reform of the Bavarian penal code which led to the abolition of torture and became a model for several other countries. ...

, and the brother of philosopher

Ludwig Feuerbach Ludwig Andreas von Feuerbach (; 28 July 1804 – 13 September 1872) was a German anthropologist and philosopher, best known for his book ''The Essence of Christianity'', which provided a critique of Christianity that strongly influenced gener ...

. After receiving his doctorate at age 22, he became a professor of

mathematics Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...

at the Gymnasium at

Erlangen Erlangen (; East Franconian German, East Franconian: ''Erlang'', Bavarian language, Bavarian: ''Erlanga'') is a Middle Franconian city in Bavaria, Germany. It is the seat of the administrative district Erlangen-Höchstadt (former administrative d ...

. In 1822 he wrote a small book on mathematics noted mainly for a theorem on the

nine-point circle In geometry, the nine-point circle is a circle that can be constructed for any given triangle. It is so named because it passes through nine significant concyclic points defined from the triangle. These nine points are: * The midpoint of eac ...

, which is now known as

Feuerbach's theorem In the geometry of triangles, the incircle and nine-point circle of a triangle are internally tangent to each other at the Feuerbach point of the triangle. The Feuerbach point is a triangle center, meaning that its definition does not depend on th ...

. In 1827 he introduced

homogeneous coordinates In mathematics, homogeneous coordinates or projective coordinates, introduced by August Ferdinand Möbius in his 1827 work , are a system of coordinates used in projective geometry, just as Cartesian coordinates are used in Euclidean geometry. T ...

, independently of Möbius.

Works

* . ("Properties of some special points in the plane of a triangle, and various lines and figures determined by these points: an analytic-trigonometric treatment") *''Grundriss zu analytischen Untersuchungen der dreyeckigen Pyramide ''("Foundations of the analytic theory of the triangular pyramid")

References

External links

* *
Feuerbach's Theorem: a Proof

* {{DEFAULTSORT:Feuerbach, Karl Wilhelm 1800 births 1834 deaths Writers from Jena People from Saxe-Weimar German Lutherans 19th-century German mathematicians Geometers