Parallelograms have several properties. Using one of these properties, we can define a parallelogram as a quadrilateral with two pairs of parallel sides. We can use the other properties to show that a quadrilateral is a parallelogram.
According to Theorem 6.9, we can prove that a quadrilateral is a parallelogram if we show that both pairs of opposite sides are congruent.
According to Theorem 6.10, we can prove that a quadrilateral is a parallelogram if we show that both pairs of opposite angles are congruent.
According to Theorem 6.11, we can prove that a quadrilateral is a parallelogram if we show that its diagonals bisect each other.
According to Theorem 6.12, we can prove that a quadrilateral is a parallelogram if we show that one pair of opposite sides is both parallel and congruent.
