Question

* If the base of a cone of 21 cm diameter and 12 cm oblique height is semicircular, then the total surface area is __________. *

1️⃣ 1098 sq. Cm
2️⃣ 1089 sq. Cm
3️⃣ 1079 sq. Cm
4️⃣ 1099 sq cm​

Answer 1

Given : base of a cone of 21 cm diameter and 12 cm oblique height is  hemispherical

To Find :   total surface area

1️⃣ 1098 sq. Cm

2️⃣ 1089 sq. Cm

3️⃣ 1079 sq. Cm

4️⃣ 1099 sq cm​

Solution:

total surface area  = CSA of Cone  + CSA of  Hemisphere

CSA of Cone  = πRL

R = 21/2 cm

L = 12

π = 22/7

CSA of Cone    = (22/7)(21/2)12

= 396  cm²

CSA of Hemisphere  = 2πR²

= 2(22/7)(21/2)²

= 693   cm²

total surface area is 396  + 693

Correct Option is

=  1089    cm²

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