RUSSELL KIGHTLEY / SCIENCE PHOTO LIBRARY RUSSELL KIGHTLEY / SCIENCE PHOTO LIBRARY
Sphere area as a cylinder. Animation showing how the area of a sphere of radius 'r' can be represented as the curved surface area of a cylinder of length '2r' and radius 'r'. The unrolled curved surface area of the cylinder has a length of '2r' and a height equal to the circumference of the cylinder ('2r' multiplied by the mathematical constant 'pi'). The area of a sphere is these two values multiplied to produce 4'pi'r (four times 'pi' times the radius squared).
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