Davies, Charles, 1798-1876 · New York and Chicago, A. S. Barnes and company · leaf 125
llelogram, and EF will be equal and parallel to CD.Then, since AB and EF are both parallel to CD, they willbe parallel to each other (Th. x); and since they are eachequal to CD, they will be equal to each other. Hence, thefigure BAEF is a parallelogram (Bk. 1. Th. xxv), and conse-quently, AE is… … THEOREM XII. If tu?o planes are parallel, a straight line vihich is perpendicularto the one will also be perpendicular to the oilier. BOOK v 123 Of Plane M Let MN and PQ be two par-allel planes, and let AB be per-pendicular to MN: then will itbe perpendicular to PQ. For, draw any line, BC, in…
Geometry · Plane trigonometry
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