Answer:
AD is a transversal between these sides, so ∠A and ∠D are supplementary angles.
Explanation:
Supplementary angles are two or more angles that sum up to
. And a parallelogram has opposite side to be parallel and equal. With the sum of interior angles to be
.
Given that: AB∥DC
<A and <D are consecutive angles of the parallelogram.
AD is the transversal of the interior angles A and D, so that the addition of <A and <D gives the sum of angles on a straight line.
Therefore, AD is a transversal between these sides, so ∠A and ∠D are supplementary angles.