Tanner, J. H. (John Henry), b. 1861, Allen, Joseph · New York, American Book Co · leaf 201
ndso on. The points thus foundevidently satisfy the defini-tion of the parabola [Art. 79].If these are then connectedby a smooth curve, it will beapproximately the requiredparabola. (2) By a continuously mov-ing point. Let DD be thedirectrix and F the focus.Place a right triangle with itslonger… … Fig. 78. 112,113] THE PARABOLA 185 point be pressed against the string, keeping it taut while thetriangle is moved along the directrix, as indicated in the figure,then, in every position of P, FP=KP, therefore the pencil will trace an arc of a parabola. 113. Subtangent and subnormal. Construction…
Geometry, Analytic
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