### Theory:

A parallelogram is a flat shape with four sides in which opposite sides parallel and equal in length.

Where $$|$$ and $$||$$ denotes equal sides.

Properties of parallelogram:
• Opposite sides are parallel.
• Opposite sides are equal in length.
• Opposite angles are equal. (Angles $$A$$ and $$D$$ are same and angles $$B$$ and $$C$$ are same.)
• Angles "$$A$$" and "$$C$$"  or "$$B$$" and "$$D$$" add up to $$180°$$ so that they are supplementary angles. (For example, Two angles ($$140°$$ and $$40°$$) are supplementary angles because they add up to $$180°$$).
• Adjacent angles are supplementary in parallelogram.
Important!
For example: A parallelogram became a rectangle where all angles are right angles.