Question:
If the area of the base of a right circular cone is 3850 cm2 and its height is 84 cm, then find the slant height of the cone.
Solution:
We have,
Height $=84 \mathrm{~cm}$
Let the radius and the slant height of the cone be $r$ and $l$, respectively.
As,
Area of the base of the cone $=3850 \mathrm{~cm}^{2}$
$\Rightarrow \pi r^{2}=3850$
$\Rightarrow \frac{22}{7} \times r^{2}=3850$
$\Rightarrow r^{2}=3850 \times \frac{7}{22}$
$\Rightarrow r^{2}=1225$
$\Rightarrow r=\sqrt{1225}$
$\therefore r=35 \mathrm{~cm}$
Now,
$l=\sqrt{h^{2}+r^{2}}$
$=\sqrt{84^{2}+35^{2}}$
$=\sqrt{7056+1225}$
$=\sqrt{8281}$
$=91 \mathrm{~cm}$
So, the slant height of the given cone is 91 cm.