2. If both pairs of opposite sides of a quadrilateral are
congruent, then the quadrilateral is a parallelogram.
CPCTC stands for "corresponding parts of congruent triangles are
congruent" and tells us if two or more triangles are congruent, then their
corresponding angles and sides are congruent as well.
3. 1. Prove that the opposite sides of a parallelogram are congruent
4. If a quadrilateral is a parallelogram, then it its opposite sides
are congruent.
