Young, George, jr, Baxter, Hubert Eugene, joint author · New York, The Macmillan Co. · leaf 152
ix, andEccentricity. This is a special case of § 113, which see. 123. To find the Foci of an Ellipse. From § 121 it will beseen that in Fig. 130, nf-\-nf=m. Therefore if an arc isstruck from « as a center, with a radius equal to half the majoraxis, the points / and /, where this arc cuts the axis,… … Fig. 131 Put pins at the foci and loop around them a continuous string,the length of which equals 2fv. A pencil, p, shding in the loopwill describe the required ellipse. For large size rough work,such as gardening, this method is satisfactory, but for smallor accurate constructions, the difficulty…
Geometry, Descriptive
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