Assn parallelograms:

A parallelogram is a quadrilateral with (two pairs of) opposite parallel sides.

Prove as many of these theorems as you are convinced are true:

• The opposite angles of a parallelogram are congruent
• The opposite sides of a parallelogram are congruent
• One diagonal of a parallelogram divides the parallelogram into two congruent triangles
• The two diagonals of a parallelogram divide the parallelogram into two opposite pairs of congruent triangles
• The diagonals of a parallelogram bisect each other
• A quadrilateral whose opposite sides are congruent is a parallelogram
• A quadrilateral whose diagonals bisect each other is a parallelogram.