1. In Fig. 6.28, find the values of x and y and then show that AB || CD.
Solution: We know that a linear pair is equal to 180°. So, x+50° = 180° ∴ x = 130° We also know that vertically opposite angles are equal. So, y = 130° In two parallel lines, the alternate interior angles are equal. In this, x = y = 130° This proves that alternate interior angles are equal and so, AB || CD.
