If a parallelogram is known to have one right angle, then repeated use of co-interior angles proves that all its angles are right angles. If one angle of a parallelogram is a right angle, then it is a rectangle.

How do you know if a parallelogram is a rectangle?

If the diagonals of a parallelogram are congruent, then it's a rectangle (neither the reverse of the definition nor the converse of a property). If a parallelogram contains a right angle, then it's a rectangle (neither the reverse of the definition nor the converse of a property).

Can you turn a parallelogram into a rectangle?

Genius! You made the parallelogram into a rectangle. Key intuition: Every parallelogram can be made into a rectangle, which is why we use the same formula to find the area of a parallelogram and a rectangle.