QA-Tf9: QA-5th point tangent


QA-Tf9 maps a point P into the tangent through P at the circumscribed conic of P1,P2,P3,P4,P. It is the dual of QL-Tf7.
 
Construction:
Definition of Triangle Transformation TR-Tfx:
TR-Tfx(ABC,P,Pi) = P-Isoconjugate wrt triangle ABC of P.
It can be constructed as QA-Tf2(Pi) wrt quadrangle (Pa,Pb,Pc,P) , where Pa,Pb,Pc are the vertices of the Anticevian Triangle of P wrt ABC (construction of Eckart Schmidt, see Ref-34, QFG#2145, #2148).
Let P1, P2, P3, P4 be the basic points of the Reference Quadrangle, also referred to as Pi (i=1,2,3,4). Let P be some random point. Let QA-DT = Diagonal Triangle QA-Tr1.
Then QA-Tf9(P) is the line on which P and the 4 occurrences of Pi’ = TR-Tfx(QA-DT,P,Pi) are collinear.
 
QA Tf9 5th Point Tangent 01
 
 
Table of 5th point tangents:
       where QA-Pxx = QA-P2.QA-Tf2(QA-P2) ^ QA-P4.QA-Tf2(QA-P4) = point on QA-Cu7
 
CT-Coordinates:
Let P (x : y : z) be the 5th point, then QA-Tf9(P) is

(p y z (r y - q z) : q x z (-r x + p z) : r x y (q x - p y))

Properties:
QA-Tf9(QA-Px) is the line through QA-Px, QA-Tf2(QA-Px), QA-Tf5(QA-Px).
• When QA-Px and QA-Py are involutary conjgates (QA-Tf2), then QA-Tf9(QA-Px)=QA-Tf9(QA-Py)=QA-Px.QA-Py.
• The Crosspoint(P,Pi) wrt triangle Pj.Pk.Pl (i,j,k,l are different numbers from (1,2,3,4)) lies on the 5th point tangent of P. See Ref-13, keyword Crosspoint.