Final answer:
The validity of the construction is proven by the corresponding angles theorem, the vertical angles theorem, the definition of a segment bisector, and the definition of an angle bisector.
Step-by-step explanation:
The reasons that contribute to proving the validity of the construction are:
When two lines are cut by a transversal and the corresponding angles are congruent, the lines are parallel. This is known as the corresponding angles theorem.
When two lines are cut by a transversal and the vertical angles are congruent, the lines are parallel. This is known as the vertical angles theorem.
Definition of segment bisector: If a segment is divided into two equal parts, then the line segment that divides it is called a segment bisector.
Definition of an angle bisector: If an angle is divided into two equal angles, then the line or ray that divides it is called an angle bisector.