Question

The radius of the base of a right circular cone is 21 cm and its height is 20 cm. Find the curved surface area of the cone.

• A. $3300c{m}^2$
• B. $1914c{m}^2$
• C. $1386c{m}^2$
• D. $26720c{m}^2$

Answer 1

The correct option is B $1914c{m}^2$

Given that,
Radius of right circular cone (r) = 21 cm
Height of right circular cone (h) = 20 cm

Slant height of the cone,
$l=\sqrt{r^2+h^2}$
$\Rightarrow l=\sqrt{{21}^2+{20}^2}$
$\Rightarrow l=29cm$

We know that,
Curved surface area of cone
$=\pi rl$
$=\frac{22}{7}\times 21\times 29$
$=1914c{m}^2$