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, 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 gene ...

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

Erlangen Erlangen (; East Franconian: ''Erlang'', Bavarian: ''Erlanga'') is a Middle Franconian city in Bavaria, Germany. It is the seat of the administrative district Erlangen-Höchstadt (former administrative district Erlangen), and with 116,062 inhab ...

. 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 ea ...

, 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. ...

, 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