In the given figure, line AB and CD intersect at O. If ∠COB=x∘, ∠BOD=4x∘ and ∠AOD=y∘, then y= ______ .
18∘
28∘
36∘
45∘
(i) ∠COB+∠BOD=180∘.........(linear pair) ⇒x∘+4x∘=180∘ ⇒5x∘=180∘ ⇒x=36∘ (ii) ∠AOD=∠COB .......(vertically opposite angles) ∴y=x=36∘