Posted by simran on Tuesday, December 4, 2012 at 6:35am.
The missing part is the height of the cone, but it is 2/3 the volume of the hemisphere (semi-sphere).
volume of hemisphere = (1/2 (4/3)π (21^3) = 6174π
but the volume of the cone is 2/3 of that or 4116π
vol of cone = (1/3)π r^2 h
4116π = (1/3)π(21^2)h
12348 = 441h
h = 28
Now use your formulas for surface area of a sphere, take half of that , and use your formula for the surface area of a cone with radius 21 and height 28
Make sure NOT to include the circular base joining them when finding surface area
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