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    Question

    In a circle with centre O, ABC is a secant intersecting

    the circle at A and B and DC is a tangent to the circle at D. If DC = 12 cm and BC = 6 cm, then the length of AB is equal to:
    A 20 cm Correct Answer Incorrect Answer
    B 18 cm Correct Answer Incorrect Answer
    C 22 cm Correct Answer Incorrect Answer
    D 16 cm Correct Answer Incorrect Answer

    Solution

    ATQ,

    We have, β‡’ DC = 12 cm and BC = 6 cm β‡’ DC2 = BC Γ— (BC + AB) β‡’ 122 = 6 Γ— (6 + AB) β‡’ 144 = 6 Γ— (6 + AB) β‡’ 144 = 36 + 6AB β‡’ 144 - 36 = 6AB β‡’ 108 = 6AB β‡’ AB = 108 / 6 β‡’ AB = 18 cm ∴ The length of AB is 18 cm.

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