Question: abcd is a parallelogram proof?
Answer: Proof: Given ABCD, let the diagonals AC and BD intersect at E, we must prove that AE ∼ = CE and BE ∼ = DE. The converse is also true: If the diagonals of a quadrilateral bisect each other, then the quadrilateral is a parallelogram. Theorem: Opposite angles of a parallelogram are congruent to each other.