Copy of Theorem 09 - Opposite Sides and Angles in a Parallelogram

This shows that the opposite sides of a parallelogram are always equal in length and the opposite angles are also equal.
Click and drag the side [AB] or the side [AD] to change the shape of the parallelogram.[br][br]What do you notice about the adjacent angles?[br][br]Change the diagram so that all four sides are equal in length. What is this figure called?
– Parameshwari, SeamusMcCabe

Information: Copy of Theorem 09 - Opposite Sides and Angles in a Parallelogram