In the give 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° Figure
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Solution
(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°