Question
The slant height of a right circular cone is 10 m and its height is 8 m. Find the area of its curved surface.
Answer: Option C
$$\eqalign{
& l = 10\,m,h = 8\,m \cr
& So, \cr
& r = \sqrt {{l^2} + {h^2}} \cr
& \,\,\,\, = \sqrt {{{\left( {10} \right)}^2} - {{\left( 8 \right)}^2}} \cr
& \,\,\,\, = 6\,m \cr} $$
∴ Curved surface area :
$$\eqalign{
& = \pi rl \cr
& = \left( {\pi \times 6 \times 10} \right){m^2} \cr
& = 60\pi \,{m^2} \cr} $$
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$$\eqalign{
& l = 10\,m,h = 8\,m \cr
& So, \cr
& r = \sqrt {{l^2} + {h^2}} \cr
& \,\,\,\, = \sqrt {{{\left( {10} \right)}^2} - {{\left( 8 \right)}^2}} \cr
& \,\,\,\, = 6\,m \cr} $$
∴ Curved surface area :
$$\eqalign{
& = \pi rl \cr
& = \left( {\pi \times 6 \times 10} \right){m^2} \cr
& = 60\pi \,{m^2} \cr} $$
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