###### Answer: plane

A line and a plane or two planes in three-dimensional Euclidean space that do not share a point are also said to be parallel. However two lines in three-dimensional space which do not meet must be in a common plane to be considered parallel; otherwise they are called skew lines .

Foundations of geometry is the study of geometries as axiomatic systems.There are several sets of axioms which give rise to Euclidean geometry or to non-Euclidean geometries.These are fundamental to the study and of historical importance but there are a great many modern geometries that are not Euclidean which can be studied from this viewpoint.

In the real plane a degenerate conic can be two lines that may or may not be parallel a single line (either two coinciding lines or the union of a line and the line at infinity) a single point (in fact two complex conjugate lines ) or the null set (twice the line at infinity or two parallel complex conjugate lines ).

Parallel – Wikipedia

Parallel (geometry) – Wikipedia

Parallel (geometry) – Wikipedia

Parallel (geometry) – Wikipedia

Spherical geometry is the geometry of the two-dimensional surface of a sphere.In this context the word “sphere” refers only to the 2-dimensional surface and other terms like “ball” or “solid sphere” are used for the surface together with its 3-dimensional interior.

The term can take on several different meanings depending on the context. For example: In various branches of mathematics certain concepts are introduced as primitive notions (e.g. the terms “point” ” line ” and “angle” in geometry). As these terms are not defined in terms of other concepts they may be referred to as ” undefined terms “.

One variable. Frequently the term linear …