Angle 1 is congruent to angles 3, 5, and 7. We know this because vertical angles are congruent (angle 3), as are corresponding angles (angle 5) and alternate exterior angles (angle 7).
Angle 3 is congruent to angles 1, 5, and 7. We know this because vertical angles are congruent (angle 1), as are corresponding angles (angle 7) and alternate interior angles (angle 5).
Angle 4 is congruent to angles 2, 6, and 8. We know this because vertical angles are congruent (angle 2), as are corresponding angles (angle 8) and alternate interior angles (angle 6).