The semi-vertical angle of a cone is 45o. If the height of the cone is 20.025, then its approximate lateral surface area is
A
401√2π
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B
400√2π
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C
399√2π
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D
none of these
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Solution
The correct option is A401√2π Here r=lsinα ⇒r=l√2 from the figure given below h=lcosα ⇒l=20.025√2 Lateral surface area of coneS=πrl ⇒S=πl2√2 ⇒S=401√2π sq.units