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Surface area of a cone - class-X
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The lateral surface area (in ${cm}^{2}$) of a cone with height $3$ cm and radius $4$ cm is:
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A
$62\cfrac{6}{7}$
💡 Explanation:
Curved surface area of a cone $= \pi rl$, where $r$ is the radius of the cone and $l$ is the slant height.
For a cone, $l = \sqrt { { h }^{ 2 }+ {r}^{ 2 } } $, where $h$ is the height.
Hence, $ l = \sqrt { { 3 }^{ 2 }+ {4}^{ 2 } } $
$ l = \sqrt {25} $
$ l = 5 $ cm
Hence, Curved surface area of this cone, $ =\displaystyle \frac {22}{7} \times 4 \times 5 = 62 \frac {6}{7} {cm}^{2} $