Question

angle theorem: if two
lines are cut by a, then
alternate interior angles are.
conversely, if two lines are cut by a and
alternate interior angles are, then the lines
have to be.

Explanation:

The Alternate Interior Angle Theorem describes the relationship between parallel lines cut by a transversal and their alternate interior angles, with a converse stating the condition for lines to be parallel based on congruent alternate interior angles.

Answer:

Angle Theorem: If two parallel lines are cut by a transversal, then alternate interior angles are congruent.
Conversely, if two lines are cut by a transversal and alternate interior angles are congruent, then the lines have to be parallel.