Editing Conical surface (section)

==Special cases==
If the directrix is a circle <math>C</math>, and the apex is located on the circle's ''axis'' (the line that contains the center of <math>C</math> and is perpendicular to its plane), one obtains the ''right circular conical surface'' or [[Double cone (geometry)|double cone]].<ref name=msg/> More generally, when the directrix <math>C</math> is an [[ellipse]], or any [[conic section]], and the apex is an arbitrary point not on the plane of <math>C</math>, one obtains an [[elliptic cone]]<ref name=young/> (also called a ''conical quadric'' or ''quadratic cone''),<ref name=osg>{{citation
 | last1 = Odehnal | first1 = Boris
 | last2 = Stachel | first2 = Hellmuth
 | last3 = Glaeser | first3 = Georg | author3-link = Georg Glaeser
 | contribution = Linear algebraic approach to quadrics
 | doi = 10.1007/978-3-662-61053-4_3
 | isbn = 9783662610534
 | pages = 91–118
 | publisher = Springer
 | title = The Universe of Quadrics
 | year = 2020}}</ref> which is a special case of a [[quadric|quadric surface]].<ref name=young>{{citation|title=Analytical Geometry|first=J. R.|last=Young|publisher=J. Souter|year=1838|page=227|url=https://archive.org/details/analyticalgeome00youngoog/page/n243}}</ref><ref name=osg/>