The main problem considered is: Given a set of linear inequalities (1.1) Ax + By = or d, which defines a set of (x;y), find and concisely define a set Y of y such that if (x;y) solves (1.1) then y belongs to Y and, conversely, if y belongs to Y then there exists an x such that (x;y) solves (1. 1). The solution to this problem involves finding the set of all extreme rays of the convex cone wA = O, w = or O and a method is given for this. The method is compared with other methods for finding extreme rays and points and finally some practical applications are given.