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    Question

    Length of a chord in a circle of radius 'r' cm, is 18 cm

    and distance between chord and centre of the circle is 40 cm. Find the value of (3r + 7).
    A 120 Correct Answer Incorrect Answer
    B 130 Correct Answer Incorrect Answer
    C 140 Correct Answer Incorrect Answer
    D 150 Correct Answer Incorrect Answer

    Solution

    Image
    AB is the chord of circle.
    Perpendicular line joining the centre of circle and chord, bisects the chord.
    i.e. AC = BC = (18/2) = 9 cm
    By Pythagoras theorem,
    OA 2 = OC 2 + AC 2
    Or, r 2 = 40 2 + 9 2
    Or, r 2 = 1600 + 81
    Or, r 2 = 1681
    So, 'r' = 41
    But length cannot be negative. So, 'r' = 41
    Required value = 3 X 41 + 7 = 130

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