In the given figure, a transversal intersects two lines AB and CD such that

x + 50° = 180° (Linear pair axiom)

⇒ x = 180° – 50°

= 130° y = 130° (Vertically opposite angles)

Therefore, ∠x = ∠y = 130° (Alternate angles)

∴ AB || CD (Converse of alternate angles axiom) **Proved.**