Question

Find the curved surface area(in $c{m}^2$) of a cone of radius $21$ cm and height $28$ cm. Take $\pi =\frac{22}{7}$

Answer 1

Curved surface area of cone $=\pi rl$

$\Rightarrow$ $l=\sqrt{h^2+r^2}$

$\Rightarrow$ $l=\sqrt{(28{)}^2+(21{)}^2}$

$\Rightarrow$ $l=\sqrt{784+441}$

$\Rightarrow$ $l=\sqrt{1225}$

$\therefore$ $l=35cm$

Curved surface area of cone $=\pi rl$

$=\frac{22}{7}\times 21\times 35$

$=2310$