If a quadrilateral has two sides that are parallel and two sides that are congruent, then the quadrilateral must be a parallelogram.
If the interior angles of a polygon add up to
, then the polygon must be a quadrilateral.
Review the Math Notes for information about the interior angles of polygons.
If a quadrilateral has
right angles, then the quadrilateral must be a rectangle.
If the diagonals of a quadrilateral bisect each other, then the quadrilateral must be a rhombus.