conical

surface

A surface generated by a moving straight line that passes through a point and keeps intersecting with a fixed curve. This fixed point is called the vertex of the cone; A fixed curve is called the directrix of a cone; The moving straight line is called the straight generatrix of the cone. When the directrix is a circle, the resulting cone is called a cone. In particular, if the vertex is on a straight line passing through the center of the circle and perpendicular to the plane of the circle, the resulting cone is called a straight cone (or straight cone). A straight conical surface can also be regarded as a moving straight line passing through a fixed point O on a fixed straight line G and keeping a fixed angle A (acute angle) with the fixed straight line. The fixed point O is its vertex, the fixed straight line G is its axis, and the fixed acute angle A is its half vertex angle. Generally speaking, a cone with an ellipse, hyperbola and parabola on the plane as the directrix and a point outside the plane as the vertex is called a cone, and its standard equation is generally. In the spatial rectangular coordinate system, the quadratic homogeneous equations about X, Y and Z always represent a quadric surface with the origin as the vertex.