In fact, by the theorem discussed in DesarguesInvolution3.html , the involution f defined on an arbitrary line through C intersecting t' at X

Similarly, taking a second line through C we find a fifth point Y on the conic and reduce the problem to the standard one of construction of a conic passing through five points: {A,B,C,D,E}.

Similarly can be handled the case of the conic passing through points {A,B,C} and being tangent to to given lines {t,t'}, t passing through A, but t' not passing through any of the given points.

In that case we draw line BC intersecting t, t' at X

CrossRatio0.html

DesarquesInvolution.html

DesarquesInvolution2.html

DesarquesInvolution3.html

HomographicRelation.html

HomographicRelationExample.html

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