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    Question

    The area of the base of a right circular cone is 81π

    cm² and its height is 12 cm. What is the curved surface area (in cm2) of the cone?
    A 1 Correct Answer Incorrect Answer
    B 2 Correct Answer Incorrect Answer
    C 3 Correct Answer Incorrect Answer
    D 4 Correct Answer Incorrect Answer

    Solution

    The area of the base of a right circular cone is 81π cm πr2 = 81π ⇒ r2 = 81 ⇒ r = 9 The height of the cone is 12 cm The slant height of the cone (l) is AC =√ (92 + 122) ⇒ AC = 15 The curved surface area of the cone is π × 9 × 15 ⇒ 135π ∴ The curved surface area of the cone is 135π cm2

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