Davies, Charles, 1798-1876 · New York and Chicago, A. S. Barnes and company · leaf 37
nal dividesthe parallelogram into two equal triangles. Cor. 1. If one angle of a parallelogram be a right angle,each of the angles will also be a right angle, and the parallelo-gram will be a rectangle. Cor. 2. Hence, also, the sum of either two adjacent anglesof a parallelogram, will be equal to… … Let ABCD be a quadrilateral, havingits opposite sides respectively equal, viz.AB=CD and AD=BC then will these sides be parallel, and thefigure will be a parallelogram. For, draw the diagonal BD. Then, the two triangles A BI)BDC, have all the sides of the one equal to all the sides ofthe other, each…
Geometry · Plane trigonometry
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