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SanuByahut
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The slant height of the frustum of a cone is 4 cm and the perimeters of its circular ends are 18 cm and 6 cm. Find the curved surface of the frustum.

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In this question we have to find the curved
surface area of frustum given that the slant
height of the frustum of a cone is 4 cm and
the perimeters of its circular ends are 18 cm and 6 cm.

This question is from r d sharma class 10 maths.
I found this question while doing mensuration of
class 10.
I need help in getting the solution.

 

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1 Answer

  1. Given,

    Slant height of frustum of cone (l) = 4 cm

    Let ratio of the top and bottom circles be r1 and r2

    And given perimeters of its circular ends as 18 cm and 6 cm

    ⟹ 2πr1 = 18 cm; 2πr2 = 6 cm

    ⟹ πr1= 9 cm and πr2 = 3 cm

    We know that,

    Curved surface area of frustum of a cone = π(r1 + r2)l

    = π(r1 + r2)l

    = (πr1+πr2)l = (9 + 3) × 4 = (12) × 4 = 48 cm2

    Therefore, the curved surface area of the frustum = 48 cm2

     

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