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
the diagonalAC, it makes the angles ACD andCAB equal, since they are altern-ate intenor angles (15^). Con-ceive the quadrilateral dividedin this diagonal into two tri-angles, as in (b). Reverse thetriangle ACB and place it as in(c). Draw DB. Since angle DCA= angle CAB, and DC = BA, ifCBA be… … Therefore, AD is parallel to BC (149). PROPOSITION X. 240, Tlieoveni,—If the opjjosite sides of a quadrilateral 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…
Geometry · Trigonometry
Internet Archive · California Digital Library · Public Domain Mark 1.0. Free to use for anything.
