§1. Descartes in his Geometria shows how the solution may be made to depend on the intersections of two conies C and C′; an account of this method is given in the Algebra of Maclaurin. Thus the roots of x4 + qx2 + rx + s = 0 are the x-coordinates of the points common to the parabola y = x2 and the circle x2 + Y2 + rx + (q – 1) y + s = 0.