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A simple (non-self-intersecting) quadrilateral is a parallelogram if and only if any one of the following statements is true: [2] [3] Two pairs of opposite sides are parallel (by definition). Two pairs of opposite sides are equal in length. Two pairs of opposite angles are equal in measure. The diagonals bisect each other.
Isosceles trapezium (UK) or isosceles trapezoid (US): one pair of opposite sides are parallel and the base angles are equal in measure. Alternative definitions are a quadrilateral with an axis of symmetry bisecting one pair of opposite sides, or a trapezoid with diagonals of equal length. Parallelogram: a quadrilateral with two pairs of ...
Every rhombus has two diagonals connecting pairs of opposite vertices, and two pairs of parallel sides. Using congruent triangles, one can prove that the rhombus is symmetric across each of these diagonals. It follows that any rhombus has the following properties: Opposite angles of a rhombus have equal measure.
The areas S and T of some two opposite triangles of the four triangles formed by the diagonals satisfy the equation = +, where K is the area of the quadrilateral. [16]: Thm.8 The midpoints of two opposite sides of the trapezoid and the intersection of the diagonals are collinear. [16]: Thm.15
The two points P and P ' (red) are antipodal because they are ends of a diameter PP ', a segment of the axis a (purple) passing through the sphere's center O (black). P and P ' are the poles of a great circle g (green) whose points are equidistant from each (with a central right angle).
The two line segments connecting opposite points of tangency have equal length. The tangent lengths, distances from a point of tangency to an adjacent vertex of the quadrilateral, are equal at two opposite vertices of the quadrilateral. (At each vertex, there are two adjacent points of tangency, but they are the same distance as each other from ...
The two bimedians of a quadrilateral (segments joining midpoints of opposite sides) and the line segment joining the midpoints of the diagonals are concurrent and are all bisected by their point of intersection. [3]: p.125 In a tangential quadrilateral, the four angle bisectors concur at the center of the incircle. [4]
An antiparallelogram is a special case of a crossed quadrilateral, with two pairs of equal-length edges. [3] In general, crossed quadrilaterals can have unequal edges. [3] A special form of the antiparallelogram is a crossed rectangle, in which two opposite edges are parallel. [4]