Question

The total surface area of cone, if its slant height is $9m$ and the radius of its base is $12m$ is:

• A. $525$ $c{m}^2$
• B. $792$ $c{m}^2$
• C. $684$ $c{m}^2$
• D. $412$ $c{m}^2$

Answer 1

The correct option is B $792$ $c{m}^2$

We know that the total surface area $S$ of a right circular cylinder of radius $r$ and slant height $l$ is given by:

$S=\pi r^2+\pi rl=\pi r(r+l)$.

Here, $r=12m$ and $l=9m$.
$\therefore S=\{\frac{22}{7}\times 12\times (12+9)\}{m}^2=792m^2$.

Therefore, option $\left(B\right)$ is correct.