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    Question

    O is the circum centre of the isosceles ∆ ABC. Given

    that AB = AC = 5 cm and BC = 6 cm. The radius of the circle is
    A 3.015 cm Correct Answer Incorrect Answer
    B 3.205 cm Correct Answer Incorrect Answer
    C 3.025 cm Correct Answer Incorrect Answer
    D 3.125 cm Correct Answer Incorrect Answer

    Solution

    Use PGT in ∆OBD r2 - (4 – r)2 = 9 (r+4-r)(r-4+r) = 9 4(2r – 4) = 9 2r – 4   = 9/4 2r = 9/4 + 4 = 25/4 r = 25/8 => 3.125 cm

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