A circular sheet of radius 18 centimetre is divided into 9 equal sectors. Find the measure of the central angle of a sector. Find the slant height of a cone which can be made by a sector. Find the lateral surface area of the cone thus formed.
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(a) central angle of a sector , θ = 360°/number of divisions of circular sheet
= 360°/9 = 40°
(b) slant height of cone which can be made by a sector, l = radius of circular sheet = 18cm
(c) radius of cone = r
we know, θ = l/r
⇒40° × π/180° = 2πR/r
⇒2π/9 = 2π × 18cm/r
⇒r = 2cm
hence, radius of cone is 2cm.
now lateral surface area of cone = πrl
= 22/7 × 2 × 18 cm²
= 792/7 cm²
= 113.14 cm²
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