In the given figure, AB and CD are two intersecting chords of a circle. If ∠CAB=40∘and∠BCD=80∘ then ∠CBD=?
(a) 80∘
(b) 60∘
(c) 50∘
(d) 70∘
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Solution
ANSWER: ( b ) 60° We have: ∠CDB = ∠CAB = 40° (Angles in the same segment of a circle) In Δ CBD, we have:∠CDB + ∠BCD +∠CBD = 180° (Angle sum property of a triangle) ⇒ 40° + 80° + ∠CBD = 180° ⇒ ∠CBD = (180° - 120°) = 60°