Yes adjacent angles of a parallelogram are supplementary
Let us consider Parallelogram ABCD.
To prove: ∠A + ∠B = 180 degrees, ∠C + ∠D = 180 degrees
AB ∥ CD and AD is a transversal.
We know that interior angles on the same side of a transversal are supplementary.
Therefore, ∠A + ∠D = 180°
Similarly, ∠B + ∠C = 180°, ∠C + ∠D = 180° and ∠A + ∠B = 180°.
Therefore, the sum of any two adjacent angles of a parallelogram is equal to 180°.
Hence, it is proved that any two adjacent or consecutive angles of a parallelogram are supplementary.