Given: 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.
To find: the curved surface of the frustum.
For the given frustum:
Slant height, l = 4 cm
Perimeter of its circular ends = 18 cm and 6 cm
Let radius of larger and shorter ends be 'r' and 'R' resp., then
Perimeter of larger circular end = 2 π r = 18 cm
⇒ π r = 9
Similarly, 2π R = 6
⇒ π R = 3
Curved surface of the frustum = (π r +π R) × l
= (9 + 3) × 4
= 12 × 4
= 48 cm2
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