#antiparallel

• Antiparallel — Being oriented in the same mathematical or geometric direction, but in a strictly opposite sense; a geometric element, vector, or straight line whose vector orientations mutually cancel each other out through direction reversal. In plane geometry, the term defines two lines that intersect two sides of an angle in such a way that they form equal but antipositioned angles relative to a symmetrical axis or a reference secant.
• Antiparallel line — A straight line that intersects the sides of a given angle in such a way that it forms with them an inverted triangle relative to the symmetry of a classic parallel line. This structural arrangement causes the angle formed by the antiparallel with one side to be perfectly equal to the angle formed by the base line with the other side, having important applications in the study of the antiparallel lines theorem in a triangle.
• Antiparallelogram — A convex or self-intersecting quadrilateral in which the opposite sides are equal in pairs, but, unlike a classic parallelogram, one pair of opposite sides intersects, creating a perfect axial symmetry. This structural arrangement provides the geometric figure with remarkable optical and mechanical properties, being frequently used in the design of linkage mechanisms where circular motion must be transformed into rectilinear motion.