<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Euclidean geometry is a mathematical system attributed to the Alexandrian Greek mathematician Euclid, which he described in his textbook on geometry: the Elements . Euclid's method consists in assuming a small set of intuitively appealing axioms, and deducing many other propositions (theorems) from these . Although many of Euclid's results had been stated by earlier mathematicians, Euclid was the first to show how these propositions could fit into a comprehensive deductive and logical system . The Elements begins with plane geometry, still taught in secondary school as the first axiomatic system and the first examples of formal proof . It goes on to the solid geometry of three dimensions . Much of the Elements states results of what are now called algebra and number theory, explained in geometrical language . </P> <P> For more than two thousand years, the adjective "Euclidean" was unnecessary because no other sort of geometry had been conceived . Euclid's axioms seemed so intuitively obvious (with the possible exception of the parallel postulate) that any theorem proved from them was deemed true in an absolute, often metaphysical, sense . Today, however, many other self - consistent non-Euclidean geometries are known, the first ones having been discovered in the early 19th century . An implication of Albert Einstein's theory of general relativity is that physical space itself is not Euclidean, and Euclidean space is a good approximation for it only where the gravitational field is weak . </P>

Who worked out a system of plane geometry