Math CentralQuandaries & Queries


Question from Brenda, a student:

What is the surface area of a hemisphere with a radius of 2 inches?

Hi Brenda,

The surface area of a sphere of radius $r$ inches is $4 \pi r^2$ square inches where $\pi$ is approximately $3.14159.$ The surface of a hemisphere is composed of two parts, the curved, dome shaped part (green in my diagram) and the flat part (blue in my diagram).


The flat part is a circle of radius $r$ inches and it has area $\pi r^2.$ Hence the surface area of the hemisphere is half the surface area of the sphere plus the area of the circular base.


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