Lateral Surface Area of Cone: The curved surface area of a cone is also called the lateral surface area. Lateral surface area of cone
where r = radius of the base of the cone and l = slant height of the cone and
Illustration: The circumference of the base of a 10m height conical tent is 44m. Calculate the length of canvas used in making the tent if width of canvas is 2m.
Solution: Given: Circumference of cone = 44 m and h =10m and breadth = 2 m
So, we have, = 44m ..............(i)
So, Using equation (i), we have
As we know Area of Canvas = Curved Surface Area of Cone
Area of Canvas = length x breadth = length x 2 ...................(ii) [As breadth = 2 m]
= 12.2 m
Now, using equation (ii), we have
Area of Canvas = length x 2
length
Length of canvas =
Illustration: The radius and slant height of a cone are in the ratio 4 : 7. If its curved surface area is 792 sq cm, find its radius. (Use )
Solution: Let r cm be the radius and l cm the slant height of the cone. Then,
r : l = 4 : 7
Let the common factor = x
cm and cm ........................(i)
Now, curved surface area = 792 sq cm
But x = - 3 is not possible.
Hence, x = 3
Using x = 3 in equation (i), we have
cm
Hence radius of the base of the cone is 12 cm.