Complex quadrilaterals
A self-intersecting quadrilateral is called variously a cross-quadrilateral, crossed quadrilateral, butterfly quadrilateral or bow-tie quadrilateral. In a crossed quadrilateral, the four "interior" angles on either side of the crossing (two acute and two reflex, all on the left or all on the right as the figure is traced out) add up to 720°.[10]
- Crossed trapezoid (US) or trapezium (Commonwealth):[11] a crossed quadrilateral in which one pair of nonadjacent sides is parallel (like a trapezoid)
- Antiparallelogram: a crossed quadrilateral in which each pair of nonadjacent sides have equal lengths (like a parallelogram)
- Crossed rectangle: an antiparallelogram whose sides are two opposite sides and the two diagonals of a rectangle, hence having one pair of parallel opposite sides
- Crossed square: a special case of a crossed rectangle where two of the sides intersect at right angles
Special line segments
The two diagonals of a convex quadrilateral are the line segments that connect opposite vertices.
The two bimedians of a convex quadrilateral are the line segments that connect the midpoints of opposite sides.[12] They intersect at the "vertex centroid" of the quadrilateral (see § Remarkable points and lines in a convex quadrilateral below).
The four maltitudes of a convex quadrilateral are the perpendiculars to a side—through the midpoint of the opposite side.[13]
https://en.wikipedia.org/wiki/Quadrilateral#Complex_quadrilaterals
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