Gore, James Howard, 1856-1939 · New York, Longmans, Green, and co. · leaf 171
ngles on thesame side of the secant plane is equal to two right diedralangles; and conversely. 6. Two diedral angles whose faces are parallel each to eachare either equal or together equal to two right diedral angles. 7. Diedral angles are to each other as their plane angles;hence the plane angle… … Let the planes PQ and RS be perpendicular to MN. To prove that their intersection AB is perpendicular to MN. Let a perpendicular be erected to the plane MN at B. Since B is a point in the plane RS, as RS is perpendicularto MN, the perpendicular BA will lie (by 365) in RS. For the same reason BA…
Geometry
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