Page 5 - Lesson Notes-Ch.13 SA and Volumes(Cone)

Let the radius (r) = 4x

Height (h) = 7x

Now, C. S. A = 792
22 × 4 × 7 = 792
7
2
⟹ 88x = 792
2
⟹ x = 792 = 9
88
⟹ x =√9 = 3

Therefore Radius = 4x = 4 ×3 = 12 cm

Example: 6
A right circular cone is 84 cm high and the radius of its base is 35 cm. Find the
volume of the cone.

Solution:
1
2
Volume of cone =  r h
3

Example: 7

Find the volume of a cone, the circumference of whose base is 132 cm and
whose height is 15.5 cm.

Solution.
For the cone, h = 15.5 cm circumference = 132 cm.

= 3 7 = 21 cm
Therefore, volume of the cone

= 7161 cm
3
5