# Anti-parallel straight lines

From Encyclopedia of Mathematics

*with respect to two given lines and *

Two straight lines and which intersect and so that (cf. Fig.).

Figure: a012660a

If and are anti-parallel with respect to and , then and are also anti-parallel with respect to and . In any quadrilateral inscribed in a circle, any two opposite sides are anti-parallel with respect to the other two sides. If the lines and intersect at a point , one also says that and are anti-parallel with respect to the angle . If the lines and coincide, and are said to be anti-parallel with respect to a straight line.

**How to Cite This Entry:**

Anti-parallel straight lines.

*Encyclopedia of Mathematics.*URL: http://encyclopediaofmath.org/index.php?title=Anti-parallel_straight_lines&oldid=13704

This article was adapted from an original article by A.B. Ivanov (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article