Angle A is congruent to angle D in rectangle ABCD because corresponding angles in congruent figures are equal.
In the provided diagram, since line AB is perpendicular to line AD, we know that ∠A is a right angle, which measures 90 degrees.
In the same way, since line CD is perpendicular to line AD, it means that ∠D is also a right angle, measuring 90 degrees.
This implies that both angles A and D are right angles. Two angles are congruent if they have the same measure.
Since both ∠A and ∠D have the same measure of 90 degrees, they are congruent.