Given: w ∥ x and y is a transversal. Prove: ∠3 and ∠5 are supplementary. Parallel and diagonal lines w and x are cut by horizontal transversal y. On line w where it intersects with line y, 4 angles are created. Labeled clockwise, from uppercase left, the angles are: 1, 3, 4, 2. On line x where it intersects with line y, 4 angles are created. Labeled clockwise, from uppercase left, the angles are: 5, 7, 8, 6. Use the drop-down menus to complete the proof. Given that w ∥ x and y is a transversal, we know that ∠1 ≅∠5 by the . Therefore, m∠1 = m ∠5 by the definition of congruent. We also know that, by definition, ∠3 and ∠1 are a linear pair so they are supplementary by the . By the , m∠3 + m ∠1 = 180. Now we can substitute m∠5 for m∠1 to get m∠3 + m∠5 = 180. Therefore, by the definition of supplementary angles, ∠3 and ∠5 are supplementary.