"The Greeks studied the conic sections from a purely geometric point of view. But the invention of in the seventeenth century made the study of geometric objects, and curves in particular, increasingly part of algebra. Instead of the curve itself, one considered the equation relating the x and y coordinates of a point on the curve. It turns out that each of the conic sections is a special case of a quadratic (second-degree) equation, whose general formula is Ax2 + By2 + Cxy + Dx + Ey = F. For example, if A = B = F = 1 and C = D = E = 0 we get the equation x2 + y2 = 1, whose graph is a [[w:Unit circle|[unit] circle]]... The ... corresponds to the case A = B = D = E = 0 and C = F = 1; its equation is xy = 1 (or equivalently y = 1/x), and its s are the x and y axes."