The height and radius of a cone are in ratio 21 : 7. The area of base is 154 sq.cm. Find the lateral surface area of the cone.
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Let the height of cone be 21x.
and the radius of cone be 7x.
A/Q,
Area of base = ∏r²
154=22×7x×7x/7
154×7=22×7×7×x²
∴ x=1
Height=21cm
radius=7cm
Slant height=√7²+21²
=7√10cm
L.S.A of cone=∏RL
=22×7×7√10/7
=154√10cm²
and the radius of cone be 7x.
A/Q,
Area of base = ∏r²
154=22×7x×7x/7
154×7=22×7×7×x²
∴ x=1
Height=21cm
radius=7cm
Slant height=√7²+21²
=7√10cm
L.S.A of cone=∏RL
=22×7×7√10/7
=154√10cm²
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