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    Question

    The base of a right pyramid is a square of side 10 cm.

    If its height is 10 cm. then the area (in cm2) of its lateral surface is:
    A 50 √5 Correct Answer Incorrect Answer
    B 100 Correct Answer Incorrect Answer
    C 100 √5 Correct Answer Incorrect Answer
    D 100( √5 + 1) Correct Answer Incorrect Answer

    Solution

    Slant height = EF Height = EO = 10 cm OF = 10/2 = 5 cm In ΔEOF, EF^2 = OE^2 + OF^2 ⇒ 10^2 + 5^2 ⇒ EF = √125 = 5√5 Slant height = EF = 5√5 cm Perimeter of the base = 4 × 10 = 40 cm Lateral surface = (1/2) × Perimeter of the base × Slant height ⇒ (1/2) × 40 × 5√5 ⇒ 100√5 cm^2

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