| 释义 |
parallel In Euclidean geometry, two or more lines or planes that are always equidistant from one another, however far they are extended. Consequently they will never meet, though this is not a sufficient condition for lines in three dimensions to be parallel, as skew lines also never meet. Two parallel lines have to lie in a plane. Sometimes curves or surfaces are described as parallel if they satisfy the equidistant condition, where the distance between the curves or surfaces is defined as the shortest distance from a point on one curve or surface to any point lying on the other.
In the hyperbolic plane, two lines are said to be parallel if they do not meet. No two lines are parallel in the elliptic plane. |