Question

The radius of the base of a cone is 9 cm and its height is 40 cm. What is its curved surface area? What is its total surface area? (π = 3.14)

Answer 1

Radius of cone (r) = 9 cm
Height of cone (h) = 40 cm
The height and radius of a cone form a right angle.
Let the slant height be l cm.
By Pythagoras Theorem,
l² = r² + h²
⇒ l² = 9² + 40²
⇒ l² = 81 + 1600
⇒ l² = 1681
⇒ l² = 41 cm

Curved surface area of a cone = πrl
= 3.14 × 9 × 41
= 1158.66 Sq cm
Total surface area of a cone = πr(l + r)
= 3.14 × 9 × (9 + 41)
= 3.14 × 9 × 50
= 1413 Sq cm