Question

find the total surface area of a cone if its slant height is 21 m and diameter of its base is 24m​

Answer 1

Answer:

slant height of cone is l=21 m.

 diameter of its base is d=24 m.

hence, radius of its base is r= $\frac{d}{2}$

=12 m

now, the total surface area of cone is given by

$s = \pi(rl + {r}^{2} ) \\ s = \pi(12 \times 21 + {(12)}^{2} ) \\ s = \pi(252 + 144) \\ s = \frac{22}{7} \times 396 \\ s = 244.57 m {}^{2}$

hence, S =1244.57 m²

Answer 2

• Total surface area of cone is 1244.57 m².

Step-by-step explanation:

Given:-

• Slant height of cone is 21 m.
• Diameter of base of is 24 m.

To find:-

• Total surface area of cone.

Solution:-

Radius = Diameter/2

= 24/2

= 12

Radius of cone is 12 m.

We know,

Total surface area of cone = πr² + πrl

Where,

• r is radius of cone.
• l is slant height of cone.

Put r and l is formula :

$\longrightarrow$ π × (12)² + π × (12) × 21

$\longrightarrow$ 22/7 × 12 × 12 × 22/7 × 12 × 21

$\longrightarrow$ 3168/7 + 792

$\longrightarrow$ 452.57 + 792

$\longrightarrow$ 1244.57

Therefore,

Total surface area of cone is 1244.57 m².