Archimedes - OTSC - I - Proposition 39

The surface of the solid figure circumscribed about the sector of the sphere [excluding its base] will be greater than that of the sector of the sphere.
Corollary : The surface of the figure so described about the sector of the sphere is equal to a circle the square on whose radius is equal to the rectangle AB x (BB' + CC' + ... + KK' + LL'/2)
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