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    Question

    A person from the top of a hill observes a vehicle

    moving towards him at a uniform speed. It takes 10 minutes for the angle of depression to change from 45° to 60°. After this the time required by the vehicle to reach the bottom of the hill is
    A 12 min 20 sec Correct Answer Incorrect Answer
    B 13 min Correct Answer Incorrect Answer
    C 13 min 40 sec Correct Answer Incorrect Answer
    D 13 min 40 sec Correct Answer Incorrect Answer

    Solution

    [tan 45° = 1] [tan Q = P/B] [tan 60° = √3 / 1] = (√3 – 1) = 10 min = 1 → (10 / √3 – 1) = (10 / √3 – 1) × (√3 + 1) / (√3 + 1) = (10(√3 + 1)) / 2 = 5(√3 + 1) = 5√3 + 5 = 5 × 1.732 + 5 = 8.66 + 5 => 13.66 = 13 min 40sec Ans

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