The first six books of the elements of Euclid : with a commentary and geometrical exercises ; to which are annexed a treatise on solid geometry, and short essays on ancient geometrical analysis, and the theory of transversals (1861)
Lardner, Dionysius, 1793-1859 · London : Print. for Taylor and Walton · leaf 61
d H K.F remain equal. It is evident that their supplementsC IB and GRF are also equal. (118) Cor. 2.—If a line be perpendicular to one of two parallel lines,it will be also perpendicular to the other; for the alternate anglesmust be equal. (119) Cor. 3.—The parts of all perpendiculars to two… … to the two triangles, the sides A C and B D must be equal (XXVI). (120) Cor. 4.—If two angles be equal (A B C and D E F)sides A B and D E be parallel, and the other sides B Cand E F lie at the same side of them, they will also beparallel; for draw B E. Since A B and D E are parallel,the angles G B…
Geometry
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