AB is the diameter and AC is a chord of a circle such that BAC=30∘ . If tangent at C intersects AB produced in D, prove that BC=BD.
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Solution
∠DCB=∠BAC=30∘ (angle bet tangent & chord BC = angle the opp segment) ∠ACB=90∘ (angle is semicircle) ∴∠CBA=60∘(fromΔABC∠CBA=∠BCD+∠CDB60∘=30∘+x⇒∠CDB=30∘∴ΔCBDisisocells∠BCD=∠CDB=30∘ ⇒BC=BD Proved