Question

The total surface area of a cone of radius r/2 and length 2l, is
A. 2πr(l+r)
B. πr (l + r/4)
C. πr(l+r)
D. 2πrl

Answer 1

Given : Radius of a cone = r/2  

Length = 2l

T.S.A of cone = πr(l + r)  

T.S.A of cone = π × r/2 (2l + r/2)

T.S.A of cone = πr/2(2l + r/2)

T.S.A of cone = 2πrl/2 + πr²/4

T.S.A of cone = πrl + πr²/4

T.S.A of cone = πr(l + r/4)

Hence,  the total surface area of a cone is  πr(l + r/4)

Option (B) πr(l + r/4) is correct.

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Answer 2

Solutions :

T.S.A of cone = πr(l + r)  

T.S.A of cone = π × r/2 (2l + r/2)

T.S.A of cone = πr/2(2l + r/2)

T.S.A of cone = 2πrl/2 + πr²/4

T.S.A of cone = πrl + πr²/4

T.S.A of cone = πr(l + r/4)