An elementary treatise on modern pure geometry (1893)
Lachlan, Robert · London, New York, Macmillan and Co. · leaf 73
conciurent. 101. Any two lines AX, AX, drawn so that the angle XAXhas the same bisectors as the angle BAC are said to be isogonalconjugates with respect to the angle BAC. Let AX, BY, CZ be the straight lines connecting the verticesof the triangle ABC to any point 0, and let AX, BY, GZ be 56… … But since AX, BY, GZ are concurrent, the latter product isequal to unity. Hence by § 99, it follows that AX, BY, GZ arealso concurrent. Thus: when three lines drawn through the vertices of a triangleare concurrent, their isogonal conjugates with respect to the anglesat these vertices are also…
Geometry
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