Find the relation between the lines in image 4.

In image 4, we have two lines, 'a' and 'b', intersected by a transversal line 'c'. The angle between line 'c' and line 'a' is labeled as α (alpha), and the angle between line 'c' and line 'b' is labeled as 180° - α. Since the sum of the angles α and 180° - α is α + (180° - α) = 180°, these two angles are supplementary.

If two lines are intersected by a transversal such that the consecutive interior angles are supplementary, then the lines are parallel.

Therefore, lines 'a' and 'b' are parallel.