By applying a projectivity that sends P, Q to two points at infinity, AA'C'C becomes a parallelogram, B* becomes its center and the theorem reduces to the exercise handled in MenelausApp.html .

Considering the pair of lines (a,b) as a degenerate conic, the theorem represents a special case of Pascal's theorem.

Notice that lines a, b, c have a common point (O) exactly in the case AA', BB' and CC' are restricted to pass trhough a common point (P). In that case line c is the polar of P with respect to the two lines a and b. The following figure illustrates this.

Hint: triangles AA'C*, CC'A* are then point-perspective and the theorem of Desargues applies etc..(see Desargues.html ).

Pappus line c is simply the

Desargues.html

LineHomographyAxis.html

Menelaus.html

MenelausApp.html

PappusLines2.html

PappusSelfDual.html

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