
Jon S. answered 04/29/21
Patient and Knowledgeable Math and English Tutor
Let P be point of intersection of AC and BD.
Two diagonals intersecting form two pairs of vertical angles: <BPA and <CPD; < BPC and <APD.
AP = PC and BP = PB by definition of bisect.
You can prove opposite tringles BPA and CPD are congruent by SAS and opposite sides AB = CD by CPCTE
You can prove opposite triangles BPC and APD are congruent by SAS and opposite sides BC = AD by CPCTE.
Since opposite sides of the quadrilateral are equal, the quadrilateral by definition is a parallelogram.