The missing angle (a) formed by a transversal intersecting a line segment is 73 degrees, congruent to the given angle due to the alternate interior angle relationship in parallel lines.
When a transversal intersects a pair of parallel lines, alternate interior angles are congruent. In this case, the given angle formed between the line segment and the transversal is 73 degrees. Therefore, the corresponding alternate interior angle is also 73 degrees.
So, the measure of the missing angle (a) is also 73 degrees. This is due to the property of alternate interior angles formed by a transversal and two parallel lines. In essence, the angles on the same side of the transversal and between the two lines are equal.
In summary, the missing angle (a) is 73 degrees, maintaining congruence with the given angle of 73 degrees, as dictated by the alternate interior angle relationship in parallel lines cut by a transversal.