Question

You are trying to prove that quadrilateral ABCD is a rhombus. You know that both pairs of opposite sides are parallel (a parallelogram). Which additional fact would prove that ABCD is a rhombus?

Answer 1

The diagonals are perpendicular

Answer 2

Quadrilateral ABCD would be a rhombus if all sides of the quadrilateral are also equal in length. Also add on the fact that none of the angles are right angles.