Alternate interior angles are 3 and 6.
Alternate interior angles are angles that are on opposite sides of the transversal and inside the parallel lines.
Alternate interior angles are congruent, which means that they have the same measure. This is a theorem in geometry that can be proven using the properties of parallel lines and transversals.
Angle 3 is located inside line AD and on the opposite side of the transversal from angle 6. Angle 6 is located inside line HE and on the opposite side of the transversal from angle 2. Therefore, angle 3 and angle 6 are a pair of alternate interior angles.
Angles a and b are alternate interior angles because they are on opposite sides of GH and inside the parallel lines AD and HE.