# The slant height

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.

Solution:

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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