Quadrilaterals

 

This picture demonstrates Theorems 5-1 to 5-6. All of these rectangles have opposite sides that are congruent and opposite angles that are congruent. Both pairs of these quadrilaterals are also congruent, making the quadrilaterals parallelograms. Last, this picture demonstrates Theorem 5-6, saying that if both pairs of opposite angles of a quadrilateral are congruent then the quadrilateral is a parallelogram. (~DF5)