What do we call a quadrilateral with one pair of sides parallel?
Rectangle the following: A rectangle is a special case of a parallelogram in which each pair of adjacent sides is perpendicular. A parallelogram is a special case of a trapezium (known as a trapezoid in North America) in which "both" pairs of opposite sides are parallel and equal in length. A trapezium is a convex quadrilateral which has at least one pair of parallel opposite sides. A convex quadrilateral is De Villiers defines a rectangle more generally as any quadrilateral with axes of symmetry through each pair of opposite sides. This definition includes both right-angled rectangles and crossed rectangles. Each has
Newton's theorem (quadrilateral) four triangles. Newton's theorem (quadrilateral) In Euclidean geometry Newton's theorem states, that in any tangential quadrilateral other than a rhombus the center of its incircle lies on its Newton line. Let "ABCD" be a tangential quadrilateral with at most one pair of parallel sides. Furthermore, let "E" and "F" the midpoints of its diagonals "AC" and "BD" and "P" be the center of its incircle. Given such a configuration the point P is located on the Newton line, that is line "EF" connecting the midpoints of the diagonals. A tangential quadrilateral with two pairs of parallel sides is a rhombus.