Question

Find the total surface area of a cone whose radius is r/2 and slant height is 21.

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Answer 1

Step-by-step explanation:

The answer is B.

Given, radius,

R=r/2

and slant height,

L=21

∴

Total surface area of a cone Is given in the image shown above

Answer 2

Here the slant height and radius of a cone are given

Radius = r / 2

slant height = 21

We have to find the total surface area of the cone

Total surface area of cone = πR( R + l )

                                            = (22/7) × (r/2) ( r/2 + 21 )

                                             = (11r/7) ( 0.5r + 21 )

                                             = 0.786r² + 33r

Hence, the total surface area of the cone will be 0.786r² + 33r square units.