### Theory:

A parallelogram is a flat shape quadrilateral with 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 the same, and angles $$B$$ and $$C$$ are the same.)
• Adjacent angles are supplementary. Angles $$A$$ and $$B$$ or $$C$$ and $$D$$ add up to $$180°$$.
Important!
A parallelogram can be a square, rectangle, and rhombus with some conditions.

For example, A parallelogram became a rectangle where all angles are right angles.