Question

Find the total surface area of a cone whose radius is $12$ m and the slant height is $23$ m.

• A. $420\pi {\text{mm}}^2$
• B. $420\pi {\text{cm}}^2$
• C. $420\pi {\text{m}}^2$
• D. $420\pi \text{m}$

Answer 1

The correct option is C $420\pi {\text{m}}^2$

Total surface area of cone is $S=\pi r(r+l)$.

Here, radius is $r=12$ m and slant height is $l=23$ m.

Thus,

$S=\pi r(r+l)=\pi \times 12(12+23)=12\pi \times 35=420\pi$ m${}^2$

Hence, the total surface area of the cone is $420\pi$m${}^2$.

Therefore, option $C$ is correct.