Given:
Height = 24 m
Slant height = 30 m
Formula used:
The curved surface area of Cone = 1/2 × (perimeter of base) × (slant height)
⇒ π × r × l
Where π = 22/7
r = radius of cone
l = slant height of the cone
The relation between r, h, and l is given by the Pythagoras theorem,
⇒ l2 = r2 + h2
Here, h = height of the cone
Calculation:
l = 30 m, h = 24 m
We know the Pythagorean triplet = (3, 4, 5)
If we multiply the triplet by 6, we get
⇒ (3 × 6, 4 × 6, 5 × 6) = (18, 24, 30)
According to the question,
h = 24 m, l = 30 m and r = 18 m
Now, the curved surface area of the cone
⇒ π × r × l
⇒ 22/7 × 18 × 30
⇒ 1697.143 m2
∴ The curved surface area of the given cone is 1697.143 m2.
Alternate Method l = 30 m, h = 24 m
Using Pythagoras theorem, l2 = r2 + h2
⇒ 302 = r2 + 242
⇒ r2 = 302 - 242 = 900 - 576 = 324
⇒ r = √324 = 18 m
Now, the curved surface area of the cone
⇒ π × r × l ⇒ 22/7 × 18 × 30
⇒ 1697.143 m2
∴ The curved surface area of the given cone is 1697.143 m2.
Important PointsPythagoras theorem: The square of the hypotenuse of a right-angled triangle is equal to the sum of the squares of the other two sides. i.e.,
(AC)2 = (AB)2 + (BC)2
Where AC = hypotenuse of the triangle
AB and BC are the other two sides of the triangle
The numbers which satisfy this relation, are called Pythagorean triplets.
e.g., (3, 4, 5), (5, 12, 13), (7, 24, 25), (8, 15, 17), (9, 40, 41), (11, 60, 61), (12, 35, 37), (16, 63, 65), (20, 21, 29), (28, 45, 53), (33, 56, 65)
All the multiples (or submultiples) of Pythagorean triplets also satisfy the relation. e.g., (6, 8, 10), (15, 36, 39) etc.