An elementary treatise on modern pure geometry (1893)
Lachlan, Robert · London, New York, Macmillan and Co. · leaf 143
ler figure F. Thus let a, b, c, d be the four sides of any tetragram, and let ustake for our axis of perspective a line parallel to the diagonaljoining the points ac, bd. Then if we suppose the line corre-sponding to this diagonal in the new figure to be at infinity, it iseasy to see that the new… … For the lines a, c are parallel to the line joining 0 to the pointac, and b, d are parallel to the line joining 0 to the point bd. 200. Ex. 1. Show that the lines joining any point to the oppositevertices of a tetragram form a pencil in involution. Ex. 2. Show that the middle points of the…
Geometry
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