Which statement explains how you could use coordinate geometry to prove the diagonals of a quadrilateral are perpendicular?

Use the slope formula to prove the slopes of the diagonals are the same.
Use the slope formula to prove the slopes of the diagonals are opposite reciprocals.
Use the distance formula to prove the lengths of the diagonals are the same.
Use the distance formula to prove the midpoints of the diagonals are the same.