The radii of the circular ends of a solid frustum of a cone are 18 cm

1.	The radii of the circular ends of a solid frustum of a cone are 18 cm and 12 cm and its height is 8 cm. Find its total surface area. [Use π= 3.14]
Answer» Height of frustum = h = 8 cm Radius of lower circular end = r = 12 cm Radius of upper circular end = R = 18 cm Let l = slant height Slant height = l² = (R-r)² + h² cm = 36 + 64 = 100 or l = 10 cm We know, Total surface area of frustum = πr² + πR² + π(R + r)l cm² = π × 12² + π × (18 + 12) × 10 cm² = 3.14(144 + 324 + 300) = 2411.52 Total surface area of frustum is 2411.52 cm²

The radii of the circular ends of a solid frustum of a cone are 18 cm and 12 cm and its height is 8 cm. Find its total surface area. [Use π= 3.14]

Answer»

Height of frustum = h = 8 cm

Radius of lower circular end = r = 12 cm

Radius of upper circular end = R = 18 cm

Let l = slant height

Slant height = l² = (R-r)² + h² cm

= 36 + 64

= 100

or l = 10 cm

We know, Total surface area of frustum = πr² + πR² + π(R + r)l cm²

= π × 12² + π × (18 + 12) × 10 cm²

= 3.14(144 + 324 + 300)

= 2411.52

Total surface area of frustum is 2411.52 cm²