Question:
The height of a cone 21 cm. Find the area of the base if the slant height is 28 cm.
Solution:
It is given that:
Height of the traffic cone (h) = 21 cm
Slant height of the traffic cone (l) = 28 cm
Now we know that,
$\mathrm{I}^{2}=\mathrm{r}^{2}+\mathrm{h}^{2}$
$28^{2}=r^{2}+21^{2}$
$r^{2}=28^{2}-21^{2}$
$r=\sqrt{77} \mathrm{~cm}$
Area of the circular base $=\pi r^{2}$
$=\frac{22}{7} *(7 \sqrt{7})^{2}=1078 \mathrm{~cm}^{2}$
Therefore the area of the base is $1078 \mathrm{~cm}^{2}$