The measures of the adjacent angles of a parallelogram add up to be 180 degrees, or they are supplementary. Then, AD ∥ BC and AB is a transversal. Similarly, ∠B + ∠C = 180°, ∠C + ∠D = 180° and ∠D + ∠A = 180°. Thus, the sum of any two adjacent angles of a parallelogram is 180°.Click to see full answer. Besides, how do you prove an angle is supplementary?You must prove that the sum of both angles is equal to 180 degrees. (“If two angles form a linear pair, then they are supplementary; that is, the sum of their measures is 180 degrees.”)Also, are adjacent angles supplementary in a trapezium? Every trapezium shows the following properties: Angle: The sum of angles in a trapezoid-like other quadrilateral is 360°. Two angles on the same side are supplementary, that is the sum of the angles of two adjacent sides is equal to 180°. Its diagonals bisect with each other. Also know, are adjacent angles of a quadrilateral supplementary? Adjacent angles are supplementary. Diagonals bisect each other and each diagonal divides the parallelogram into two congruent triangles. If one of the angles of a parallelogram is a right angle then all other angles are right and it becomes a rectangle.How many angles can be supplementary?Supplementary Angles. Two Angles are Supplementary when they add up to 180 degrees.