Question

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

Answer 1

48cm2 curved surface area of frustum

Answer 2

Answer:

The Curved surface area of the frustum = 48 cm².

Step-by-step explanation:

SOLUTION :  

Given :  

Slant height of the frustum of a cone, l = 4 cm

Perimeter of its circular ends are 18 cm and 6cm

Let r1 and r2 be the radius of the bottom and top of the circle.

Circumference (Perimeter) of Bottom of  circle = 2πr1

18 = 2πr1

πr1 = 18/2 = 9  

πr1 = 9 cm……………(1)

Circumference (Perimeter) of top of  circle = 2πr2

6 = 2πr2

πr2 = 6/2 = 3

πr2 = 3 cm…………..(2)

Curved surface area of the frustum  = (πr1 + πr2)l

= (9 + 3) × 4

= 12 × 4 = 48 cm ²

Hence, the Curved surface area of the frustum = 48 cm².

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