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Question Measure the sides of each of these two quadrilaterals A and B. What do you notice?
Are there any pairs of sides that are equal? Which pairs are equal—adjacent or opposite?
Quadrilaterals whose opposite sides are equal are called parallelograms.
What types of angles do quadrilaterals A and B have? Which angles are equal in each of the above parallelograms?
In parallelogram A, opposite angles are equal.
In parallelogram B, all angles are equal and are right angles. Such a parallelogram is called a rectangle.
A rectangle is a special type of parallelogram.