Davies, Charles, 1798-1876 · New York and Chicago, A. S. Barnes and company · leaf 122
ich the lines meet theplane EF Then, because the lines AB, CD, are perpendicular to theplane EF, they will be perpendicular to the line BD (Def. 1).Now, if BA and DC are not parallel, they will meet at somepoint as 0 : then, the triangle OBD would have two rightangles, which ie impossible (Bk. I.… … THEOREM VI. If two planes intersect each other at right angles, and a linebo drawn in one plane perpendicular to the common intersectiontthis line will be perpendicular to the other plane. Let the plane FE be perpen-dicular to MN, and AP be drawnm the plane FE, and perpen-dicular to the common…
Geometry · Plane trigonometry
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