九章算術
The abstract concept of negative numbers was recognized as early as 100–50 BC in China. "The Nine Chapters on the Mathematical Art" contains methods for finding the areas of figures; red rods were used to denote positive coefficients, black for negative. The first reference in a Western work was in the 3rd century AD in Greece. Diophantus referred to the equation equivalent to (the solution is negative) in "Arithmetica", saying that the equation gave an absurd result.