What are the angles called that are on opposite sides of the transversal but are both interior angles?

The angles that are located on opposite sides of the transversal and are both interior angles are known as alternate interior angles. These angles are formed when a transversal crosses two parallel lines, creating pairs of angles. The key characteristic of alternate interior angles is that they are on opposite sides of the transversal, while both remaining within the boundaries set by the two parallel lines.

This property is crucial in geometry, especially when proving the parallelism of lines or solving problems involving angle relationships. The congruence of alternate interior angles is often used as a fundamental principle in geometric proofs, particularly in the context of parallel lines cut by a transversal. This contrasts with the other types of angles mentioned; for example, vertical angles are formed by intersecting lines and are opposite each other, while corresponding angles occur on the same side of the transversal and are in matching positions relative to the parallel lines.