Carl Anton Bretschneider

Carl Anton Bretschneider (27 May 1808 – 6 November 1878) was a mathematician from Gotha, Germany. Bretschneider worked in geometry, number theory, and history of geometry. He also worked on logarithmic integrals and mathematical tables. He was one of the first mathematicians to use the symbol $\backslash gamma$ for Euler's constant when he published his 1837 paper. He is best known for his discovery of Bretschneider's formula for the area of a general quadrilateral on a plane,

$A\; =\; \backslash sqrt\; \{(s-a)(s-b)(s-c)(s-d)\; -\; abcd\; \backslash cdot\; \backslash cos^2\; \backslash left(\backslash frac\{\backslash alpha\; +\; \backslash gamma\}\{2\}\backslash right)\},$

where, $a,\; b,\; c,$ and $d$ are the sides of the quadrilateral, $s\; =\; \backslash frac\{a\; +\; b\; +\; c\; +\; d\}\{2\}$ is the semiperimeter, and $\backslash alpha$ and $\backslash gamma$ are two opposite angles.

He is the son of Karl Gottlieb Bretschneider, a theologian. Provided by Wikipedia