Question: prove that adjacent angles of a parallelogram are supplementary?
Answer: Prove that any two adjacent angles of a parallelogram are supplementary. Then, AD ∥ BC and AB is a transversal. Similarly, ∠B + ∠C = 180°, ∠C + ∠D = 180° and ∠D + ∠A = 180°. ... Hence, any two adjacent angles of a parallelogram are supplementary.