Kenison, Ervin, Bradley, Harry Cyrus, 1871-1936 · New York : The Macmillan Company · leaf 196
Fig. 255. XVIII, § 154] TAXGEXT LIXES AXD PLANES 175 153. Tangents to Plane Curves. A straight line tangent to aplane curve lies in the plane of the curve. Hence, if it is required to draw a straight line tangent to aplane curve, from a point not on the curve, there is no solutionunless the given… … Fig. 256. Fig. 257. For example, Fig. 256 represents the projections of a planecurve C (§ 151), and of two points a and b. A line tangentto the curve C cannot be drawn from the point a, since it isobvious that a is not in the plane of the curve. Why ? Onthe other hand, the point b lies in the plane…
Geometry, Descriptive
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