Osgood, William F. (William Fogg), 1864-1943, Graustein, William C. (William Caspar), 1888-1941, joint author · New York : The Macmillan Company · leaf 536
a plane M is projectedon a second plane M, the area of the projected region equalsA cos 0, where 0 is the acute angle between M and M.* In the case of a rectangle whose sides are respectivelyparallel and perpendicular to the line of intersection of Mand M, the proof is immediate. For, when the… … The area A of an arbitrary region in M is the limit ap-proached by the sum B of the areas of rectangles, of the typejust described, which are inscribedin the region: A = lim B, If A is the area of the projectedregion and B is the sum of theareas of the projected rectangles,evidently A = lim B\ J…
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