Incidence (geometry) - Determining The Line Passing Through A Pair of Points

Determining The Line Passing Through A Pair of Points

Let P1 and P2 be a pair of points, both in a projective plane and expressed in homogeneous coordinates:

Let g−1 be the inverse duality mapping:

which maps points onto their dual lines. Then the unique line passing through points P1 and P2 is L3 where

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