Kenison, Ervin, Bradley, Harry Cyrus, 1871-1936 · New York : The Macmillan Company · leaf 197
anecontaining the two rectilinear elements passing through thepoint. 156. The Normal. The normal to a surface at any point on it is the straight line perpendicularto the tangent plane at that point.For certain curved surfaces, forexample, the sphere shown in Fig.258, the normal can be… … XVIII, § 157] TANGENT LINES AND PLANES 177 157. Determination of Tangent Planes by Means of the Normal.It is to be noted that the tangent plane T is absolutely deter-mined in space by means of the normal N, since but one planecan be passed through a given point a perpendicular to a givenline N. But…
Geometry, Descriptive
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