Question

In the below fig, rays AB and CD intersect at O.
 Determine y when x = 60°

Answer 1

Given x = 60°

y = ?

`∠`AOC, `∠`BOC are linear pair of angles

`∠`AOC + `∠`BOC = 180°

⇒ 2x + y = 180°

⇒  2 × 60 + y = 180°          [ ∵x = 60°]

⇒  y = 180° -120°

⇒ y = 60°

Answer 2

Rays ABand CD intersect at point O.

Therefore, ∠AOCand ∠BOCform a linear pair.

Thus,

∠AOC +∠BOC = 180°

          2x +y =180°       (1)

On substituting x = 60° :

     2x + y = 180°

2(60°) + y = 180°

    120° + y= 180°

               y = 180°- 120°

               y = 60°