Davies, Charles, 1798-1876 · New York and Chicago, A. S. Barnes and company · leaf 158
THEOREM XXII. If a regular semi-polygon he revolved about a line passingthough the centre and the vertices of two opposite angles, thesurface described by its perimeter will be equal to tlie axis -multiplied by Uie circumference of the inscribed cvrclr.. BOOK VI. 157 Of ihe Sphere … Suppose the regular semi-polygonABCDE to be revolved about the lineAF as an axis: then will the surfacedescribed by its perimeter be equal toAF multiplied by the circumference ofthe inscribed circle. From E and D, the extremities ofone of the equal sides, let fall the per-pendiculars EH, DI, on the…
Geometry · Plane trigonometry
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