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To find the radius of a sphere you first need to know what information you do have. If none, then the easiest way is to measure the volume using water displacement.
Then V = 4/3*pi*r3 so that r = cube root of 3V/4pi
The diameter is not that easy to measure because it is the distance between two parallel tangential planes to the sphere. It is very difficult to ensure that the planes are truly parallel.
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The radius of a sphere is 1/2 of its height.
Treat the 3D sphere as a 2D circle. The radius for the sphere is the same radius as for the circle. No matter where on the sphere you place a mark, the distance (radius) from the mark to the centre of the sphere will always be the same as the circle.
The surface area of the sphere with the radius doubled is 200 units2.---> Confirmed
It's the extension of the sphere's radius drawn to that point.
360 units cubed