pencil

geometry

Written and fact-checked by The Editors of Encyclopaedia Britannica

Article History

Related Topics:: projective geometry

See all related content

pencil, in projective geometry, all the lines in a plane passing through a point, or in three dimensions, all the planes passing through a given line. This line is known as the axis of the pencil. In the duality of solid geometry, the duality being a kind of symmetry between points and planes, the dual of a pencil of planes consists of a line of points. In a plane, in which there is a duality between points and lines, the dual of a line of points is the pencil of lines through a point.

This article was most recently revised and updated by William L. Hosch.