Solve this
Question:

Note Use $\pi=\frac{22}{7}$, unless stated otherwise.

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

Solution:

Slant height, l = 21 m

Radius of the base, $r=\frac{24}{2}=12 \mathrm{~m}$

$\therefore$ Total surface area of the cone $=\pi r(r+l)=\frac{22}{7} \times 12 \times(12+21)=\frac{22}{7} \times 12 \times 33=\frac{8712}{7} \mathrm{~cm}^{2}$

Thus, the total surface area of the cone is $\frac{8712}{7} \mathrm{~cm}^{2}$.