Question

The curved surface area of a cone is 792cm square and the slant height is 21.Find its radius​

Answer 1

Step-by-step explanation:

The ratio of the radius and height of the cone is 4 : 7.

Let the radius of the cone be 4x and the height be 7x

So,

Curved surface area of the cone = πrl

792 = 22/7*4x*7x

x² = (792*7)/(22*4*7)

x² = 9

x = √9

x = 3 cm

So, the radius of the cone = 4 × 3 = 12 cm.

Answer 2

Step-by-step explanation:

CSA of cone = πrl

therefore

$792 = \frac{22}{7} \times r \times 21 \\ 792 = 22 \times 3 \times r \\ r = \frac{792 }{66} \\r = \frac{132}{11} \\ r = 12$