Veblen, Oswald, 1880-1960, Young, John Wesley, 1879-1932 · Boston, New York [etc.] Ginn and Company · leaf 115
gles ABC, ABC, ABC are so related that any twoare triply perspective, the centers of perspectivity being in each case the verticesof the remaining triangle. The nine vertices of the three triangles form thepoints of one configuration of Pappus, and the nine sides form the lines ofanother… … Proof. Let n be any line on Nnot passing through A (fig. 46). Let Ol be any point not on n or on MA, and let Ax and B1 be the intersections respectively of OxA and OxB with n. Let 02 be the intersection of AA1 and BBV Then q q NAB = NA,B, = NAB.A x x A By Theorem 17 the projectivity so determined…
Geometry, Projective
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