Question

Note Use $\mathrm{\pi }=\frac{22}{7}$, 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.

Answer 1

Slant height, l = 21 m

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

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

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