Explain how to use the midpoint formula to prove or disprove that abcd is a parallelogram. a) prove that ac and bd do not have the same midpoint. the diagonals of a parallelogram cannot have the same midpoint. b) prove that ad and bc have the same midpoint. all sides of a parallelogram are congruent; therefore, they have the same midpoint. c) prove that ac and bd have the same midpoint. the diagonals of a parallelogram bisect each other; therefore, they have the same midpoint. d) prove that ab and cd do not have the same midpoint. all sides of a parallelogram are congruent; therefore, they have different midpoints.