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 130
rilateral areequal, the figure is a parallelogram. Dem.—In (a) let AB = DC, D C and AD = BC; then is ABCD aparallelogram. For, divide the quadrilateralin the diagonal AC, and revers-ing the triangle ABC, place itas in (c), and draw DB. SinceAB ^ CD, and CB = AD, DB isperpendicular to CA {130).Now,… … Fio. 181. 110 ELEMENTARY PLANE GEOMETRY. PROPOSITION XI. 241. TJieorem,—Conversely to the last, Tlie opposite sides ofa parallelogram are equal. D C Dem.—Let ABCD be a paral- lelo<rram; then AB = DC, andAD = CB. Since DC is parallel to AB, an-gle DCA= angle CAB, Also, sinceAD is parallel to BC,…
Geometry · Trigonometry
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