Davies, Charles, 1798-1876 · New York and Chicago, A. S. Barnes and company · leaf 35
al to four rightangles (Ax. 3). THEOREM XXIII The opposite sides and angles of every parallelogram are equal,each to each: and a diagonal divides the parallelogram into twoequal triangles. Let ABCD be any parallelogram, andDB a diagonal: then will the oppositesides and angles be equal to each… … BOOK 1. 30 Of Parallelograms. parallels are cut by the diagonal DB, the alternate angles willbe equal (Th. xii): that is the angle ADB^DBC and BDC=ABD. Hence the two triangles ADB BDC, having two angles inthe one equal to two angles in the other, will have their thirdangles equal (Th. xvii. Cor.…
Geometry · Plane trigonometry
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