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The slant height of a right circular cone is 10 m and its height is 8 m. Find the area of its curved surface.

a) 30π m2
b) 40π m2
c) 60π m2
d) 80π m2

Answer: c
Explanation:
$$\eqalign{ & l = 10\,m \cr & h = 8\,m \cr & So,\,r = \sqrt {{l^2} – {h^2}} = \sqrt {{{\left( {10} \right)}^2} – {8^2}} = 6\,m \cr & {\text{Curved}}\,{\text{surface}}\,{\text{area}} \cr & \pi \,rl = \left( {\pi \times 6 \times 10} \right){m^2} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\, = 60\pi \,{m^2} \cr} $$

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