A treatise on special or elementary geometry (1877)
Olney, Edward, 1827-1887, Olney, Edward, 1827-1887. Elements of trigonometry, plane and spherical · New York : Sheldon · leaf 197
e plane GB. Conceive gBperpendicular to AB. Now, let the plane revolve upon ABas an axis, whence gB describes a circle (?); and at any posi*tion of the revolving plane, as/BAF, since fBg measures theamount of revolution, it may be taken as the measure of thediedral f-Bk-g. When^-B has made i of a… … PROPOSITION 1. 4:26, TJieorem.—Any line in one face of a rigid diedral, per-pendicular to its edge, is perpendicular to the otherface, Dem.—In the face CB of the right diedral C-AB-D, let MObe perpendicular to the edge AB ; then is it perpendicular tothe face DB. For, draw ON in the face DB, and…
Geometry · Trigonometry
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