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A parallelogram has 2 sets of parallel sides. The opposite sides  are equal in length and opposite angles are equal. Examples of  parallelograms are squares, rectangles and â¦ rhombuses. You can find  the perimeter of a parallelogram by doubling the base+side length. 6 people found this useful.
2. If both pairs of opposite sides of a quadrilateral are congruent, then it is a parallelogram. 3. If one pair of opposite sides of a quadrilateral are both parallel and congruent, then it is a parallelogram. 4. If the diagonals of a quadrilateral bisect each other, then the it is a parallelogram. 5.. If both pairs of opposite angles of a quadrilateral are congruent, then it is a parallelogram. Proving That a Quadrilateral is a Rectangle One can prove that a quadrilateral is a rectangle by first showing that it is a parallelogram and then using either of the following methods to complete the proof.