Question

Find the total surface area of a cone, if its slant height is 28 cm and the diameter of its base is half of the slant height.
1. 700 cm²
2. 770 cm²
3. 777 cm²
4. 767 cm²

Answer 1

Correct Answer - Option 2 : 770 cm²

Given:

Slant height = 28 cm

Diameter = Slant height/2

Formula Used:

Radius = Diameter/2

Total surface area of cone = πr(r + l)

Calculation:

Diameter = 28/2 = 14 cm

Radius = 14/2 = 7 cm

Total surface area of cone = πr(r + l)

⇒ Total surface area of cone = π × 7(7 + 28)

⇒ Total surface area of cone = 22 × 35 = 770 cm²

∴ Total surface area of cone is 770 cm2.

The correct option is 2 i.e. 770 cm2