Alfred Marshall (1842-1924) was one of the most influential economists of his generation. His book, Principles of Political Economy (1890) brought together the theories of supply and demand, marginal utility and the costs of production[?] into a coherent whole. It was the dominant textbook in England for a long period.
... terms of the coefficients a, b and c, which are assumed to be real (but see below for generalizations) with a being non-zero. These solutions are also called ...