Manning, Henry Parker, 1859- · Boston, U.S.A., Ginn & Company · leaf 50
For an obtuse angle we may take p negative, and we have n(-p)=7r-ii(p), 6. Theorem. The perpendiculars erected at the middlepoints of the sides of a triangle are all parallel if two ofthem are parallel. … Let A, B, and C be the vertices of the triangle, and D, E,and F, respectively, the middle points of the opposite sides.Suppose the perpendiculars at D and E are given parallel, toprove that the perpendicular at F is parallel to them. 40 NON-EUCLIDEAN GEOMETRY Proof. Draw CM through C parallel to…
Geometry, Non-Euclidean
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