lalawilcher1 lalawilcher1 24-09-2020 Mathematics contestada D AB = 21 DC = 3x AD = y +7 BC = 2y Quadrilateral ABCD is a parallelogram if both pairs of opposite sides are congruent. Show that quadrilateral ABCD is a parallelogram by finding the lengths of the opposite side pairs. A) 7.3 B) 14,7 21,7 D 21, 14