# Find the total surface area of a cone, if its slant height is 21 m and diameter of its base is 24 m.

**Solution:**

Diameter is 24m and the slant height of the cone is 21m.

The total surface area of the cone is the sum of the curved surface area and area of the base which is a circle.

Curved surface area of a right circular cone of base radius 'r' and slant height 'l' is πrl.

Total surface area of the cone = πrl + πr^{2} = πr (l + r )

Diameter, d = 24m

Radius, r = 24/2m = 12m

Slant height, l = 21 m

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

= 22/7 × 12 m × (12 m + 21 m)

= 22/7 × 12 m × 33 m

= 8712/7 m²

= 1244.57 m²

Thus, total surface area of the cone = 1244.57 m².

**Video Solution:**

## Find the total surface area of a cone, if its slant height is 21 m and diameter of its base is 24 m.

### Class 9 Maths NCERT Solutions - Chapter 13 Exercise 13.3 Question 2:

Summary:

It is given that the slant height of a cone is 21 m and diameter of the base is 24 m. We have found that total surface area of the cone = 1244.57 m².