1. A parallelogram is a quadrilateral with two opposite sides parallel to each other.
2. A parallelogram has the following properties:
(1) The opposite sides of the parallelogram are parallel and equal in weight.
(2) The diagonals of parallelograms are equal.
(3) The diagonals of the parallelogram are bisected.
(4) A parallelogram is a spatial figure.
(5) In addition, it can be seen from the above definitions that the two opposite sides of a parallelogram row are parallel respectively.
3. Judgment method of parallelogram:
(1) Two sets of parallelograms whose opposite sides are equal are parallelograms.
(2) A quadrilateral whose diagonals are bisected is a parallelogram.
(3) A set of parallelogram whose opposite sides are parallel and equal is a parallelogram.
(4) Two sets of quadrangles with equal diagonals are parallelograms.
(5) Two sets of parallelograms with opposite sides parallel are parallelograms.
(6) The quadrilateral obtained by connecting the midpoints of each side of the quadrilateral in turn is called the midpoint quadrilateral. No matter how the shape of the original quadrilateral changes, the shape of the midpoint quadrilateral is always a parallelogram. The midpoint of a quadrilateral A quadrilateral is a parallelogram.