Math CentralQuandaries & Queries


Question from Mandy, a parent:

How can I show that the total surface are of any solid hemisphere is 75% of the area of the full sphere?

Hi Mandy,

The surface area of a sphere of radius $r$ units is $4 \pi \; r^2$ square units.

A hemisphere is half a sphere and its surface area is composed of two parts, the curved part which has half the surface area of the sphere and the circular flat base which is a disk of radius $r$ units. What is the area of the disk. What is the total surface area of the hemisphere?


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