Apollonius called cone the solid obtained in this way: a circle (base-circle) is lying in a plane and a point V is out of this plane; if we draw the straight line joining the point V with a point P of the circle (only the segment PV as the ancient thought) , when P moves on the circle and cover it all, the segment VP describes a cone .The axis of the cone is the line joining the point V with the centre of the base-circle. Every section of the cone with a plane containing the axis is called triangle through axis The secant plane, on which lies the conic section, and the plane of the base-circle intersect on a line perpendicular to the side of the triangle through axis.The type of conic section depends on the position of the secant plane. It is possible to prove the characteristic property of the curve ("symptom") in the 3d space.