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Question
In the below fig, rays AB and CD intersect at O
Determine x when y =40

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Solution 1
Given y = 40°, x = ?
`∠`AOC and `∠`BOC are linear pair of angles
`∠`AOC + `∠`BOC = 180°
⇒ 2x + y = 180°
⇒ 2x + 40 = 180°
⇒ 2x = 140°
⇒ x = `(140°)/2`
⇒ y = 70°
Solution 2
Rays ABand CD intersect at point O.

Therefore, ∠AOCand ∠BOCform a linear pair.
Thus,
∠AOC +∠BOC = 180°
2x +y =180° (1)
On substituting y = 40°:
2x +y = 180°
2x + 40° = 180°
2x = 180°-40°
2x = 140°
`x = (140°)/2`
x = 70°
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