A quadrilateral is considered a parallelogram if the opposite angles of the figure are congruent. This means the angles formed by two adjacent sides and the inc...
A quadrilateral is considered a parallelogram if the opposite angles of the figure are congruent. This means the angles formed by two adjacent sides and the included angle are equal. For example, consider the following quadrilateral:
ABCD
In this case, angles A and C are congruent, as are angles B and D. This means that the opposite angles of the figure are congruent, and therefore, the quadrilateral is a parallelogram